msm: vidc: fix bw voting issue for ar50

- should divide by 2 when calculating cbcr read bw.
- refine dpb/opb compression factor.
- use dpb_compression_factor instead of input_cr to
  calculate dpb_write bw.
- use actual input_cr from userspace if available.
- use actual bitrate instead of lookup table.

Change-Id: Id20cd4e87e0c20c7104e5bc4ec94d675f82ee1fb
Signed-off-by: Qiwei Liu <qiweil@codeaurora.org>