mm-video-v4l2: venc: Add support for B-frames

Allow B-frames in encode for H264 and HEVC. B-frames
are enabled by default for camcorder use-cases. Validate
intra period against system capabilities and recalibrate
GOP if required.

CRs-Fixed: 2051943
Change-Id: I3fa4579eadd544977a2d7310d90f7938f6b85ff6
2 files changed