Display events now always carry the display id they happened on

Change-Id: I12de1d883c23927722bc3a71b782f0079de4e831
diff --git a/include/gui/DisplayEventReceiver.h b/include/gui/DisplayEventReceiver.h
index 1117f95..f8267bf 100644
--- a/include/gui/DisplayEventReceiver.h
+++ b/include/gui/DisplayEventReceiver.h
@@ -48,6 +48,7 @@
 
         struct Header {
             uint32_t type;
+            uint32_t id;
             nsecs_t timestamp;
         };
 
@@ -56,7 +57,6 @@
         };
 
         struct Hotplug {
-            int32_t id;
             bool connected;
         };