drm/msm/dsi-staging: unify dynamic clk support for command mode

Currently the dynamic bit clock switch trigger for command mode
is supported via sysfs node. This might lead to unnecessary
race conditions, when dsi driver is enabling the dsi bit clock
as part of commit and at the same time if bit rate change via
sysfs happens. So make the trigger happens via kernel mode set
call as done for video mode.

Change-Id: I17acb408d2b6dbd6fa41994e56262e31e43d088b
Signed-off-by: Ritesh Kumar <riteshk@codeaurora.org>