msm_fb: display: Send vsync events using sysfs for MDP3 targets

Replace sending of vsync timestamp using uevents with sysfs entry
as uevent result in increase in power numbers due to broadcast in
nature.

Change-Id: I22cfbd68c8bcbe4a47e94074393f1cbf79920c58
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>