drm_hwcomposer: add compositor interface header

Change-Id: I4b743e442e140f8fe5452fba3dd718995fe77b1b
(cherry picked from commit af3c4ecc830bef9d538333d0bf200fed39ae3649)
diff --git a/Android.mk b/Android.mk
index c505476..820235b 100644
--- a/Android.mk
+++ b/Android.mk
@@ -37,8 +37,7 @@
 	system/core/libsync \
 	system/core/libsync/include \
 
-LOCAL_CFLAGS :=
-LOCAL_SRC_FILES := hwcomposer.cpp
+LOCAL_SRC_FILES := hwcomposer.cpp compositor.cpp
 
 ifeq ($(strip $(BUFFER_IMPORTER)),drm-gralloc)
 LOCAL_C_INCLUDES += external/drm_gralloc