common: fetch nested configuration

Config for a code updater is provided via dbus, the common
'FirmwareInfoDef' becomes a nested dbus interface.

For BIOS code updater, it looks like this:
```
xyz.openbmc_project.Configuration.BIOS.FirmwareInfo
```

Update the common code to query this configuration from the nested dbus
interface.

Tested: BIOS code updater can query its configuration with following
EM config json fragment:

```
{
  "Name": "HostSPIFlash",
  "SPIControllerIndex": 1,
  "SPIDeviceIndex": 0,
  "HasME": false,
  "Layout": "Flat",
  "Tool": "None",
  "MuxOutputs": ["BMC_SPI_SEL"],
  "MuxGPIOValues": [1],
  "FirmwareInfo": {
    "VendorIANA": "6653",
    "CompatibleHardware": "com.tyan.Hardware.S8030.SPI.Host"
  },
  "Type": "BIOS"
},
```

Change-Id: I1d7241537b759ee74ce4a1f932b5597ac7d95e52
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/common/src/software_manager.cpp b/common/src/software_manager.cpp
index 351533f..b95fcab 100644
--- a/common/src/software_manager.cpp
+++ b/common/src/software_manager.cpp
@@ -86,19 +86,21 @@
             std::string emConfigType{};
             std::string emConfigName{};
 
+            const std::string ifaceFwInfoDef = interfaceFound + ".FirmwareInfo";
+
             try
             {
                 {
                     auto propVendorIANA =
                         co_await client.call<std::variant<uint64_t>>(
-                            ctx, "Get", interfaceFound, "VendorIANA");
+                            ctx, "Get", ifaceFwInfoDef, "VendorIANA");
 
                     vendorIANA = std::get<uint64_t>(propVendorIANA);
                 }
                 {
                     auto propCompatible =
                         co_await client.call<std::variant<std::string>>(
-                            ctx, "Get", interfaceFound, "Compatible");
+                            ctx, "Get", ifaceFwInfoDef, "CompatibleHardware");
 
                     compatible = std::get<std::string>(propCompatible);
                 }