drm/msm/dsi-staging: Add support for clk switch with constant FPS

There is lag or lead in the FPS during dynamic clock change,
along with the increment or decrement in clock. So, HFP or
VFP are adjusted to ensure a constant FPS.

Change-Id: I87ba7a185104a0f5f1d13734a7e487e728d6b2c0
Signed-off-by: Lipsa Rout <lrout@codeaurora.org>
Signed-off-by: Yuan Zhao <yzhao@codeaurora.org>