msm: vidc: refine clock voting for vsp and turbo

- update vsp cycles from 0.7 to 0.5 bits/cycle per
  system team updated spec.
- don't decrement clock for turbo or when clock_voting
  is manually specified.

Change-Id: Id6ce1d87cf6f854cdee45c3504dcf15e950e2927
Signed-off-by: Qiwei Liu <qiweil@codeaurora.org>