[PORT FROM MAIN JB-MR2]refine code to support gfx buffer better

BZ: 152953

Support  RGB to YUV converting, 64 not aligned gfx buffer on MRFLD,
copy due to VP8 uncached memory. Uniformly use HAL_PIXEL_FORMAT_NV12
as final encode gfx buffer color format.

Change-Id: I8ede20798fcdbd228bf24504858b2b048d731f29
Orig-Change-Id: I769234279f3426ce2c873aa9cc9a383b606fa189
Signed-off-by: Zhao Liang <leo.zhao@intel.com>