msm: VPU: Add Chroma down-sampling support

Support down-sampling of the chroma channel in incoming video buffers.
Down-sampling can be dynamically enabled for individual buffers while
streaming.

Change-Id: If09e0f249d973a715b3cd44ca300a54335b1dce1
Signed-off-by: Ahmed Abdul-Salam <aabdulsa@codeaurora.org>