hwc: Rotate RGB layer using MDP Rotator

1. Use MDP rotator to rotate RGB layers which are rendered by software
2. Restrict total number of rotator sessions to 4 for all displays
3. Disable RGB layer rotation for all MDP versions < MDP5

Change-Id: Ie93111082dff9a16b614e9768df5d8ce83ff9e25
diff --git a/liboverlay/overlayRotator.h b/liboverlay/overlayRotator.h
index f7b44bd..e0f542c 100644
--- a/liboverlay/overlayRotator.h
+++ b/liboverlay/overlayRotator.h
@@ -210,6 +210,9 @@
 // Holder of rotator objects. Manages lifetimes
 class RotMgr {
 public:
+    //Virtually we can support as many rotator sessions as possible, However
+    // more number of rotator sessions leads to performance issues, so
+    // restricting the max rotator session to 4
     enum { MAX_ROT_SESS = 4 };
 
     ~RotMgr();