Subsampling aware allocs and bitstream

Subsampling aware allocs and bitstream

Make framebuffer allocations according to the chroma subsamping
factors in use. A bit is placed in the raw part of the frame header for
each of the two subsampling factors. This will be moved in a future
commit to make them part of the TBD feature set bits, probably only set
on keyframes, etc.

Change-Id: I59ed38d3a3c0d4af3c7c277617de28d04a001853