msm: vidc: Update msm-vidc-bw-gov formulas

Re-tune the formulas to not make any assumptions of the hardware
usecase.

Also convert a few integer divisions to fixedpoint divisions to retain
accuracy.

Formula revision: Venus_3xx.21

Change-Id: If765b02c69d8717081954c0746ca1c17c1d19e9b
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>