send PLDM event msg when state sensor changes

Add the D-Bus to event handler interface to listen all of the state
sensor PDRs and pldm should be able to send up a PLDM event msg when a
D-Bus property changes. the PlatformEventMessage command format is
defined in Table 15 in DSP0248 v1.2.0.

Tested: test with JSON
https://gist.github.com/lxwinspur/6a40abea7330c25e4d49826e890c4be9
The sendEventMsg method is successfully called and the corresponding
message is successfully sent when the D-Bus property value of the sensor
status changes.
print requestMsg Data: 80 02 0a 01 00 00 01 00 01 00 00 00(when calling
sendEventMsg method)

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I9b6d5c1403bfcaa00dbbf478f7d797cc4a40f20d
diff --git a/libpldmresponder/platform.cpp b/libpldmresponder/platform.cpp
index c017486..dff2352 100644
--- a/libpldmresponder/platform.cpp
+++ b/libpldmresponder/platform.cpp
@@ -172,6 +172,12 @@
         generateTerminusLocatorPDR(pdrRepo);
         generate(*dBusIntf, pdrJsonsDir, pdrRepo);
         pdrCreated = true;
+
+        if (dbusToPLDMEventHandler)
+        {
+            dbusToPLDMEventHandler->listenSensorEvent(pdrRepo,
+                                                      sensorDbusObjMaps);
+        }
     }
 
     // Build FRU table if not built, since entity association PDR's are built