msm: vidc: Introducing CBR_VFR upto 480p@30fps

Introducing CBR_VFR (CBR = constant bitrate, VFR = variable framerate
) upto 480p@30fps due to tighter bitrate convergence.

Change-Id: I9477761f7f0936a319dc66413a28cddb619ba0cb
Signed-off-by: Tapas Kumar Kundu <tkundu@codeaurora.org>