make struct Event layout consistent on 32/64-bit

To make struct Event have consistent memory layout between x86
and x86_64, force nsecs_t timestamp align to 64bit because it's
not true for x86.

Change-Id: I49eaddd89e10d595cf6a5130f9762b5388c96625
Signed-off-by: Fengwei Yin <fengwei.yin@intel.com>
diff --git a/include/gui/DisplayEventReceiver.h b/include/gui/DisplayEventReceiver.h
index f8267bf..a4718b9 100644
--- a/include/gui/DisplayEventReceiver.h
+++ b/include/gui/DisplayEventReceiver.h
@@ -49,7 +49,7 @@
         struct Header {
             uint32_t type;
             uint32_t id;
-            nsecs_t timestamp;
+            nsecs_t timestamp __attribute__((aligned(8)));
         };
 
         struct VSync {