msm: mdss: add reg bus vote to support different frequencies

Current reg bus vote client supports only single frequency
- 19MHz. This is not sufficient for different use cases like
hist update, pp lookup table update during suspend/resume
scenario. A client may request for higher frequency to finish
the job early and avoid glitches. A client based register
voting allows to traverse through votes from each client
and update register bus vote with max client input.

Change-Id: I4e94d1073375dbd71d9ba6268fc8c548ddb67440
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>