msm: vidc: Optimize bw calculations

Calculate DDR and LLCC bw simulteneously to avoid
redundant calculations. This reduces number of calculations
required by 50% and hence reduces cpu load.

CRs-Fixed: 2487664
Change-Id: I6e1768cd63d9b6651fbaf4a8ed8d5706929d7743
Signed-off-by: Chinmay Sawarkar <chinmays@codeaurora.org>