mdss: display: add dynamic mdp clock control for smart panel

For smart panel, the clock can be turned off during static screen
update to save power. This patch adds support to control mdp related
clocks dynamically.

Change-Id: I0328e156d5c0b42822f0f81aa0a8195159a1eeb7
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>