msm: vidc: add mbpf support for bengal

MBs per frame, i.e mbpf, is used to decide the
number of concurrent video sessions that can be
allowed.

Change-Id: I5f7abf764831753f7c54cac9a4ff132a074db454
Signed-off-by: Vikash Garodia <vgarodia@codeaurora.org>