msm: mdss: modify bus bw vote lock and count strategy

Currently bus bandwidth can happen from 2 separate contexts where commit
context does not hold lock and blindly votes bandwidth. Rather use a
single bandwidth lock and count for all contexts. This also requires
fixing a bug during ctl stop where ctl power status needs to be changed
only after bus vote has finished.

Change-Id: I4131b05195298d15a46101aa4ebb88ea2e80b3dc
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>