msm: vidc: Add support for Adaptive B

Add support to enable/disable adaptive B frames.
It is enabled by default by firmware.

CRs-Fixed: 2234389
Change-Id: Ia1cf6338430448151dd6f6f1cd93a9a967944cf2
Signed-off-by: Vaibhav Deshu Venkatesh <vdeshuve@codeaurora.org>