drm/msm/sde: add support for Cx iPeak mitigation

Every client driver participating in Cx iPeak mitigation
scheme need to-
1) Register to Cx ipeak driver.
2) Set vote for TCSR block before clock switch to fmax-threshold
or above through cx ipeak API.
3) Remove vote for TCSR block after clock switch to below
fmax-threshold through cx ipeak API

Changes are made to address the same in sde driver

Change-Id: I1275971901abd2075a4ff6f6e47fa9e71235090d
Signed-off-by: Raviteja Tamatam <travitej@codeaurora.org>