hwc: Support 4kx2k FB for Primary and External.

Add support for 4kx2k FB for primary and external panels.
Change class design to create appropriate version of FBUpdate on boot up based
on the panel resolution.

Change-Id: I216d815d9b81c610aa39e351f7b55736dfa48b43
diff --git a/liboverlay/overlayUtils.h b/liboverlay/overlayUtils.h
index f9fcca8..3b2f6d7 100644
--- a/liboverlay/overlayUtils.h
+++ b/liboverlay/overlayUtils.h
@@ -63,6 +63,10 @@
 #define DEBUG_OVERLAY 0
 #define PROFILE_OVERLAY 0
 
+#ifndef MDSS_MDP_RIGHT_MIXER
+#define MDSS_MDP_RIGHT_MIXER 0x100
+#endif
+
 namespace overlay {
 
 // fwd
@@ -297,6 +301,7 @@
     OV_MDP_BLEND_FG_PREMULT = MDP_BLEND_FG_PREMULT,
     OV_MDP_FLIP_H = MDP_FLIP_LR,
     OV_MDP_FLIP_V = MDP_FLIP_UD,
+    OV_MDSS_MDP_RIGHT_MIXER = MDSS_MDP_RIGHT_MIXER,
 };
 
 enum eZorder {