hwc/overlay: Add Color layer support in MDP Composition.

1. Color layer has a destination rectangle, RGBA color and plane
   alpha. There is no gralloc buffer. Layer flag "HWC_COLOR_FILL"
   denotes a Color layer.
2. There is no color member in HWC layer, so RGBA color value
   is passed via the "tranform" member from framework to HAL.

Change-Id: I8769fd3f5febcaf952a1456de0a4262679c9a0e4
diff --git a/liboverlay/overlay.h b/liboverlay/overlay.h
index c16f6e6..295e123 100644
--- a/liboverlay/overlay.h
+++ b/liboverlay/overlay.h
@@ -76,6 +76,7 @@
 
     void setSource(const utils::PipeArgs args, utils::eDest dest);
     void setCrop(const utils::Dim& d, utils::eDest dest);
+    void setColor(const uint32_t color, utils::eDest dest);
     void setTransform(const int orientation, utils::eDest dest);
     void setPosition(const utils::Dim& dim, utils::eDest dest);
     void setVisualParams(const MetaData_t& data, utils::eDest dest);