msm: vidc: Use input bitrate to calculate decoder bus vote

By calculating bitrate at each frame, we get a better estimate
of the BW requirements of the decode session. Thus improving
performance and power usage.

CRs-Fixed: 2451137
Change-Id: I22f0029bbb7d501340469a317e89de7eb34717c4
Signed-off-by: Chinmay Sawarkar <chinmays@codeaurora.org>