msm_fb: display: add sysfs and clock control to smart panel

This patch allows both vsync enable and disable are controlled
by framework. Driver reports vsync event to framework via sysfs.
Meanwhile, mdp related clocks are enabled by framework at vsync
enabled request and disabled by driver if there is no any display
update within specifid vsync period.

Change-Id: Ice5be3a6db5930b95bdd2f718d9256bf73936e23
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>