set vsync power hint

Change-Id: I28c2faf9ff584df3e74392712971cbcf75eb9e98
diff --git a/services/surfaceflinger/Android.mk b/services/surfaceflinger/Android.mk
index 8b16456..6f7a7e1 100644
--- a/services/surfaceflinger/Android.mk
+++ b/services/surfaceflinger/Android.mk
@@ -10,6 +10,7 @@
     DisplayHardware/DisplayHardware.cpp     \
     DisplayHardware/DisplayHardwareBase.cpp \
     DisplayHardware/HWComposer.cpp          \
+    DisplayHardware/PowerHAL.cpp            \
     GLExtensions.cpp                        \
     MessageQueue.cpp                        \
     SurfaceFlinger.cpp                      \