drm/msm/dpu: handle_frame_done() from vblank irq

Previously the callback was called from whoever called wait_for_vblank(),
but that isn't a great plan when wait_for_vblank() stops getting called,
and results in frame_done_timer expiring.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Rob Clark <robdclark@chromium.org>