fix BufferItem flatten/unflatten alignment

bug: 21370100
Change-Id: Ia3991dc591c176bdbd1d78d1804aa22777525b62
diff --git a/include/gui/BufferItem.h b/include/gui/BufferItem.h
index 000ef0e..145efe6 100644
--- a/include/gui/BufferItem.h
+++ b/include/gui/BufferItem.h
@@ -72,7 +72,13 @@
     // to set by queueBuffer each time this slot is queued. This value
     // is guaranteed to be monotonically increasing for each newly
     // acquired buffer.
-    int64_t mTimestamp;
+    union {
+        int64_t mTimestamp;
+        struct {
+            uint32_t mTimestampLo;
+            uint32_t mTimestampHi;
+        };
+    };
 
     // mIsAutoTimestamp indicates whether mTimestamp was generated
     // automatically when the buffer was queued.
@@ -84,7 +90,13 @@
     android_dataspace mDataSpace;
 
     // mFrameNumber is the number of the queued frame for this slot.
-    uint64_t mFrameNumber;
+    union {
+        uint64_t mFrameNumber;
+        struct {
+            uint32_t mFrameNumberLo;
+            uint32_t mFrameNumberHi;
+        };
+    };
 
     union {
         // mSlot is the slot index of this buffer (default INVALID_BUFFER_SLOT).