drm/rockchip: Improve analogix-dp psr handling

Remove the delayed worker, opting instead for the non-delayed
variety. Also introduce a lock to ensure we don't have races
with the worker and psr_state. Finally, cancel and wait for
the worker to finish when disabling the bridge.

Reviewed-by: Yakir Yang <ykk@rock-chips.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>