hwc: Add support for plane alpha

HWC 1.2 API passes down the plane alpha and the blending
operation to apply. Pass this information to the MDP.

Change-Id: I7fbd17345d9157aa654e4b1031ac3e26adf87f37
diff --git a/liboverlay/overlayMdp.cpp b/liboverlay/overlayMdp.cpp
index 2d88376..674e62d 100644
--- a/liboverlay/overlayMdp.cpp
+++ b/liboverlay/overlayMdp.cpp
@@ -94,13 +94,14 @@
     setSrcWhf(args.whf);
 
     //TODO These are hardcoded. Can be moved out of setSource.
-    mOVInfo.alpha = 0xff;
     mOVInfo.transp_mask = 0xffffffff;
 
     //TODO These calls should ideally be a part of setPipeParams API
     setFlags(args.mdpFlags);
     setZ(args.zorder);
     setIsFg(args.isFg);
+    setPlaneAlpha(args.planeAlpha);
+    setBlending(args.blending);
 }
 
 void MdpCtrl::setCrop(const utils::Dim& d) {