Limit #ROT-SESSIONS to 4 in LayerRotMap and RotMgr

* Limit the number of rotator sessions to 4 both in
LayerRotMap and RotMgr structures

* Make use of MDPVersion getter fuctions to check
for maxMixerWidth and maxDownScale supported by MDP

Change-Id: I27dac877807fbb4ed6fcb3500a3a318a2ef5d8b2
diff --git a/libhwcomposer/hwc_mdpcomp.h b/libhwcomposer/hwc_mdpcomp.h
index 1ebe0bd..5214ac6 100644
--- a/libhwcomposer/hwc_mdpcomp.h
+++ b/libhwcomposer/hwc_mdpcomp.h
@@ -248,7 +248,7 @@
     struct FrameInfo mCurrentFrame;
     struct LayerCache mCachedFrame;
     //Enable 4kx2k yuv layer split
-    static bool sEnable4k2kYUVSplit;
+    static bool sEnableYUVsplit;
     bool mModeOn; // if prepare happened
     bool allocSplitVGPipesfor4k2k(hwc_context_t *ctx, int index);
 };