msm: vidc: Enhance DCVS algorithm

This change enables DCVS for only 4K/H264 decoder use case.
It also enhances the current DCVS algorithm to account for
low output buffer count in case of dynamic buffer mode by
setting the low threshold completely based on output buffer
drain rate in display queue.

Change-Id: Id35d8fb685230fe5bd16666fa2b9560027b33981
Signed-off-by: Sowmya Pandiri <spandiri@codeaurora.org>