hwc: HWC 2.0 implementation

Add HWCLayer, HWCCallbacks and implement HWC2 layer functionality.

Change-Id: Ic7764e72f4cae534e68764df4cf80eb3db982071
diff --git a/common.mk b/common.mk
index 77f62b1..62bd128 100644
--- a/common.mk
+++ b/common.mk
@@ -1,6 +1,8 @@
 #Common headers
 display_top := $(call my-dir)
 
+use_hwc2 := false
+
 common_includes := $(display_top)/libqdutils
 common_includes += $(display_top)/libqservice
 common_includes += $(display_top)/libcopybit