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/device_factory.cpp b/rtu/device/device_factory.cpp
new file mode 100644
index 0000000..d707952
--- /dev/null
+++ b/rtu/device/device_factory.cpp
@@ -0,0 +1,54 @@
+#include "device_factory.hpp"
+
+#include "reservoir_pump_unit.hpp"
+
+#include <string>
+#include <vector>
+
+namespace phosphor::modbus::rtu::device
+{
+
+using ReservoirPumpUnitIntf = phosphor::modbus::rtu::device::ReservoirPumpUnit;
+
+auto DeviceFactory::getInterfaces() -> std::vector<std::string>
+{
+    std::vector<std::string> interfaces{};
+
+    auto rpuInterfaces = ReservoirPumpUnitIntf::getInterfaces();
+    interfaces.insert(interfaces.end(), rpuInterfaces.begin(),
+                      rpuInterfaces.end());
+
+    return interfaces;
+}
+
+auto DeviceFactory::getConfig(sdbusplus::async::context& ctx,
+                              const sdbusplus::message::object_path& objectPath,
+                              const std::string& interfaceName)
+    -> sdbusplus::async::task<std::optional<config::DeviceFactoryConfig>>
+{
+    auto rpuInterfaces = ReservoirPumpUnitIntf::getInterfaces();
+    if (rpuInterfaces.find(interfaceName) != rpuInterfaces.end())
+    {
+        co_return co_await ReservoirPumpUnitIntf::getConfig(ctx, objectPath,
+                                                            interfaceName);
+    }
+
+    co_return std::nullopt;
+}
+
+auto DeviceFactory::create(sdbusplus::async::context& ctx,
+                           const config::DeviceFactoryConfig& config,
+                           PortIntf& serialPort) -> std::unique_ptr<BaseDevice>
+{
+    switch (config.deviceType)
+    {
+        case config::DeviceType::reservoirPumpUnit:
+            return std::make_unique<ReservoirPumpUnit>(ctx, config, serialPort);
+        default:
+            break;
+    }
+
+    return nullptr;
+}
+
+} // namespace phosphor::modbus::rtu::device