drm/msm: rework vblank event handling in dpu_crtc

The vblank on/off calls were missing in dpu_crtc
leading to "driver forgot to call drm_crtc_vblank_off()"
warning while entering suspend state.
Also handle the state update completion event for
a crtc being disabled in current atomic commit.

This patch depends on https://www.spinics.net/lists/dri-devel/msg182402.html



Signed-off-by: Rajesh Yadav <ryadav@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>