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
10 files changed