msm: mdss: Disable dynamic clock gating for 8909.

Backlight calls through DCS fail if footswitch is disabled during
idle pc. To fix that, dynamic clock gating must be disabled in the
DSI power on path. This is important as disabling footswitch during
idle pc can enhance power saving.

Change-Id: If7e2b8957f52248bf789c43e1d0d2932a734d3cb
Signed-off-by: Sravanthi Kollukuduru <skolluku@codeaurora.org>