Add PLDM.Event Interface

This interface implements the StateSensorEvent signal. When the
PLDM daemon receives a state sensor EventMessages, it emits the
StateSensorEvent signal.The application that has subscribed to
the signal then receives the sensorEventMessage it needs.The
application needs relevant filters for the signal data.

Signed-off-by: Chicago Duan <duanzhijia01@inspur.com>
Change-Id: I615a2851c79634e8d068805140ff635c8adb41b8
diff --git a/xyz/openbmc_project/PLDM/Event.interface.yaml b/xyz/openbmc_project/PLDM/Event.interface.yaml
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+description: >
+    Implement to emit D-Bus signal for PLDM Event Messages. PLDM Event
+    Messages are PLDM monitoring and control messages that are used by
+    a PLDM terminus to synchronously or asynchronously report PLDM events
+    to a central party called the PLDM Event Receiver.
+
+    When the PLDM daemon receives a sensorEvent of type stateSensorState,
+    it emits the StateSensorEvent signal.
+
+    This signal would be used by PLDM Requester apps on the BMC, which
+    will rely on this signal to determine state changes on a connected
+    PLDM entity.
+
+    More information about PLDM Event Messages can be found at DSP0248
+    version 1.2.0 section 13.
+
+signals:
+    - name: StateSensorEvent
+      description: >
+          Signal indicating that a state sensor change EventMessage is
+          received.
+          More information about properties can be found at DSP0248 version
+          1.2.0 table 19.
+      properties:
+        - name: TID
+          type: byte
+          description: >
+            A terminus id.
+
+        - name: sensorID
+          type: uint16
+          description: >
+            The sensorID is the value that is used in PDRs and PLDM sensor
+            access commands to identify and access a particular sensor
+            within a terminus.
+
+        - name: sensorOffset
+          type: byte
+          description: >
+            Identifies which state sensor within a composite state sensor
+            the event is being returned for.
+
+        - name: eventState
+          type: byte
+          description: >
+            The event state value from the state change that triggered
+            the event message.
+
+        - name: previousEventState
+          type: byte
+          description: >
+            The event state value for the state from which the present
+            event state was entered.
+