video: msm: MDSS: Add Update Notify

Add update notify ioctl to MDSS driver. "Update notify" is able to signal
userspace processes when there has been a screen update or if there has
been a 22 second period without screen updates.

Change-Id: I90cf7f7e6650236186452c1a9f86850731ad785d
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>