msm: vidc: Determine DPB-OPB split mode based on bit depth

This includes changes in vidc driver to rely both on Luma and
Chroma bit depth to determine output2 dithering.
It also includes some other minor fixes.

Change-Id: I95d07b43763e1e89c0583e6bc80d7bfab80bf52b
Signed-off-by: Sowmya Pandiri <spandiri@codeaurora.org>