drm/msm/dsi: add flag for mode switch with fps

Change adds flag to identify dynamic mode switch with same
resolution and different fps. Block sending PPS command
if we hit this scenario, this optimizes mode switch time.

Change-Id: If5c86084cde641952fe294b512e937cfd1bb5479
Signed-off-by: Vara Reddy <varar@codeaurora.org>