rtu: implement modbus sensor read

Read the modbus device config from the Entity Manager configuration and
create the sensor interfaces for related sensor register config.

Tested:
Added new Unit test named test_sensors -
```
> meson test -t 10 -C builddir/ --print-errorlogs --wrapper="valgrind --error-exitcode=1" test_sensors
ninja: Entering directory `/host/repos/Modbus/phosphor-modbus/builddir'
[2/2] Linking target tests/test_sensors
1/1 test_sensors        OK              13.98s

Ok:                1
Fail:              0
```

Tested on Qemu using Mock Modbus Device -
```
root@ventura:~# busctl tree xyz.openbmc_project.ModbusRTU
└─ /xyz
  └─ /xyz/openbmc_project
    ├─ /xyz/openbmc_project/inventory_source
    │ ├─ /xyz/openbmc_project/inventory_source/Heat_Exchanger_12_DevTTYUSB0
    │ ├─ /xyz/openbmc_project/inventory_source/Heat_Exchanger_12_DevTTYUSB1
    │ ├─ /xyz/openbmc_project/inventory_source/Reservoir_Pumping_Unit_12_DevTTYUSB0
    │ └─ /xyz/openbmc_project/inventory_source/Reservoir_Pumping_Unit_12_DevTTYUSB1
    └─ /xyz/openbmc_project/sensors
      └─ /xyz/openbmc_project/sensors/temperature
        ├─ /xyz/openbmc_project/sensors/temperature/Reservoir_Pumping_Unit_12_DevTTYUSB0_RPU_Coolant_Inlet_Temp_C
        ├─ /xyz/openbmc_project/sensors/temperature/Reservoir_Pumping_Unit_12_DevTTYUSB0_RPU_Coolant_Outlet_Temp_C
        ├─ /xyz/openbmc_project/sensors/temperature/Reservoir_Pumping_Unit_12_DevTTYUSB1_RPU_Coolant_Inlet_Temp_C
        └─ /xyz/openbmc_project/sensors/temperature/Reservoir_Pumping_Unit_12_DevTTYUSB1_RPU_Coolant_Outlet_Temp_C

busctl introspect xyz.openbmc_project.ModbusRTU /xyz/openbmc_project/sensors/temperature/Reservoir_Pumping_Unit_12_DevTTYUSB1_RPU_Coolant_Outlet_Temp_C
NAME                                TYPE      SIGNATURE RESULT/VALUE                             FLAGS
org.freedesktop.DBus.Introspectable interface -         -                                        -
.Introspect                         method    -         s                                        -
org.freedesktop.DBus.Peer           interface -         -                                        -
.GetMachineId                       method    -         s                                        -
.Ping                               method    -         -                                        -
org.freedesktop.DBus.Properties     interface -         -                                        -
.Get                                method    ss        v                                        -
.GetAll                             method    s         a{sv}                                    -
.Set                                method    ssv       -                                        -
.PropertiesChanged                  signal    sa{sv}as  -                                        -
xyz.openbmc_project.Sensor.Value    interface -         -                                        -
.MaxValue                           property  d         nan                                      emits-change writable
.MinValue                           property  d         nan                                      emits-change writable
.Unit                               property  s         "xyz.openbmc_project.Sensor.Value.Unit.… emits-change writable
.Value                              property  d         1670.6                                   emits-change writable
```

Change-Id: I1368e8df5999b5cee9ac19d185ee110a9ecc3021
Signed-off-by: Jagpal Singh Gill <paligill@gmail.com>
diff --git a/rtu/device/reservoir_pump_unit.cpp b/rtu/device/reservoir_pump_unit.cpp
new file mode 100644
index 0000000..58debee
--- /dev/null
+++ b/rtu/device/reservoir_pump_unit.cpp
@@ -0,0 +1,68 @@
+#include "reservoir_pump_unit.hpp"
+
+#include "device_factory.hpp"
+
+#include <phosphor-logging/lg2.hpp>
+
+namespace phosphor::modbus::rtu::device
+{
+
+PHOSPHOR_LOG2_USING;
+
+static constexpr auto ModbusRDF040DSS5193E0ReservoirPumpUnitInterface =
+    "xyz.openbmc_project.Configuration.ModbusRDF040DSS5193E0ReservoirPumpUnit";
+
+static const std::unordered_map<std::string_view, config::DeviceModel>
+    validDevices = {{ModbusRDF040DSS5193E0ReservoirPumpUnitInterface,
+                     config::DeviceModel::RDF040DSS5193E0}};
+
+ReservoirPumpUnit::ReservoirPumpUnit(sdbusplus::async::context& ctx,
+                                     const config::Config& config,
+                                     PortIntf& serialPort) :
+    BaseDevice(ctx, config, serialPort)
+{
+    info("Reservoir pump unit {NAME} created successfully", "NAME",
+         config.name);
+}
+
+auto ReservoirPumpUnit::getInterfaces() -> std::unordered_set<std::string>
+{
+    return {ModbusRDF040DSS5193E0ReservoirPumpUnitInterface};
+}
+
+auto ReservoirPumpUnit::getConfig(
+    sdbusplus::async::context& ctx,
+    const sdbusplus::message::object_path& objectPath,
+    const std::string& interfaceName)
+    -> sdbusplus::async::task<std::optional<config::DeviceFactoryConfig>>
+{
+    config::DeviceFactoryConfig config{};
+
+    auto res = co_await config::updateBaseConfig(ctx, objectPath, interfaceName,
+                                                 config);
+    if (!res)
+    {
+        co_return std::nullopt;
+    }
+
+    for (const auto& [deviceInterface, deviceModel] : validDevices)
+    {
+        if (interfaceName == deviceInterface)
+        {
+            config.deviceModel = deviceModel;
+        }
+    }
+
+    if (config.deviceModel == config::DeviceModel::unknown)
+    {
+        error("Invalid device model {MODEL} for {NAME}", "MODEL", interfaceName,
+              "NAME", config.name);
+        co_return std::nullopt;
+    }
+
+    config.deviceType = config::DeviceType::reservoirPumpUnit;
+
+    co_return config;
+}
+
+} // namespace phosphor::modbus::rtu::device