display: Set and handle default csc as BT709

- Some clients don't set the csc for a layer and as a result
  HWC will error out. Avoid this by setting the default csc as
  BT709 in gralloc for RGB buffers.
- HWC will default to BT709 if clients have not set.

Change-Id: I6f2e0f5bf39d0e06450d50f9c7da6857aaff8b8f
Crs-fixed: 2218048
2 files changed