mm-video-v4l2: vidc: venc: Enable down scalar for encoding

Make changes to add an extension which can enable/disable
downscalar and also set the output width and height.
Whenever Downscalar is enabled, the output port definition
dimensions are ignored but downscalar width/height are used
as ouput width/height.

CRs-Fixed: 2064901
Change-Id: Ie15c0e0dde560baa56288981518ac77d4e3da59c
7 files changed