msm: mdss: trigger event timer on vsync boundary

Event timer does not get reschedule if it is
triggered at vsync boundary. This may cause the
issue for auto refresh case and vsync might be
delayed because event timer is off. Fix it by
triggering event timer on vsync boundary also.
This case will not be traversed for normal
kickoff.

Change-Id: I44813250525c1d516691b0a8419cc3a486acfaa0
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>