Pass fence to HWC on first use of buffer

Also do a CPU-wait on the fence before using it for GL composition.

Change-Id: I0f645a42a44803276cae11b904e5a26d65871562
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index d47f2e8..29515f0 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -120,6 +120,7 @@
     bool mCurrentOpacity;
     bool mRefreshPending;
     bool mFrameLatencyNeeded;
+    bool mNeedHwcFence;
     int mFrameLatencyOffset;
 
     struct Statistics {