msm: vidc: Add DCVS support

This change enables DCVS for 4K decoder use case thus reducing
power utilization. This is achieved by dynamically adapting
venus core clock vote to varying load conditions by monitoring
the buffer count released to and recycled from display.

Change-Id: Id0a9b4b6f5c79ba97fecd3d1d27c34832022edb3
Signed-off-by: Sowmya Pandiri <spandiri@codeaurora.org>