msm_fb: display: Send vsync events using sysfs for MDP4 targets

Replace sending of vsync timestamp using uevents with sysfs entry
as uevent result in increase in power numbers due to broadcast in
nature. Also, for smart panel, wait4vsync is removed.

Change-Id: I5219e85b837b8bab9d00a9f40c1048d2a2355194
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>