display: External display refactor

- cleans up external library
- add separate library for virtual display
- process virtual updates in its separate path
  in hwc.
- Acquire blank mutex lock for one complete drawing
  cycle

Change-Id: Ib984c578464a131ecdb27ee48960f58d68b7a5a7
diff --git a/common.mk b/common.mk
index e8a50c1..13cd6ef 100644
--- a/common.mk
+++ b/common.mk
@@ -6,6 +6,7 @@
 common_includes += hardware/qcom/display/libhwcomposer
 common_includes += hardware/qcom/display/libexternal
 common_includes += hardware/qcom/display/libqservice
+common_includes += hardware/qcom/display/libvirtual
 
 ifeq ($(TARGET_USES_POST_PROCESSING),true)
     common_flags     += -DUSES_POST_PROCESSING