drm/msm: dpu: Make legacy cursor updates asynchronous

This patch sprinkles a few async/legacy_cursor_update checks
through commit to ensure that cursor updates aren't blocked on vsync.
There are 2 main components to this, the first is that we don't want to
wait_for_commit_done in msm_atomic  before returning from atomic_complete.
The second is that in dpu we don't want to wait for frame_done events when
updating the cursor.

Changes in v2:
- None

Reviewed-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>