disp: msm: queue vblank work on disp thread during modeset

If vblank work is queued to event thread, during modeset,
there might be a case where vblank is enabled in between
resulting in vblank ref count mismatch. This change queues
vblank request to disp thread during modeset.

Change-Id: I98b87b4209e1f7f535980eef22a50df17c346c23
Signed-off-by: Yashwanth <yvulapu@codeaurora.org>