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.cpp b/liboverlay/overlay.cpp
index b095e9e..6aaf236 100644
--- a/liboverlay/overlay.cpp
+++ b/liboverlay/overlay.cpp
@@ -177,6 +177,13 @@
     mPipeBook[index].mPipe->setCrop(d);
 }
 
+void Overlay::setColor(const uint32_t color,
+        utils::eDest dest) {
+    int index = (int)dest;
+    validate(index);
+    mPipeBook[index].mPipe->setColor(color);
+}
+
 void Overlay::setPosition(const utils::Dim& d,
         utils::eDest dest) {
     int index = (int)dest;