msm: vidc: Add new bitrate modes cbr_vfr and mbr_vfr

New bitrate modes cbr_vfr and mbr_vfr are introduced in v4l2
controls. They need to be propaogated to firmware.

CRs-Fixed: 2201206
Change-Id: I6dad87c0dae8b405748671eb70a1a44d42e29570
Signed-off-by: Chinmay Sawarkar <chinmays@codeaurora.org>