drm/ingenic: Call drm_atomic_helper_shutdown() at shutdown time

Based on grepping through the source code this driver appears to be
missing a call to drm_atomic_helper_shutdown() at system shutdown
time. Among other things, this means that if a panel is in use that it
won't be cleanly powered off at system shutdown time.

The fact that we should call drm_atomic_helper_shutdown() in the case
of OS shutdown/restart comes straight out of the kernel doc "driver
instance overview" in drm_drv.c.

Since this driver uses the component model and shutdown happens at the
base driver, we communicate whether we have to call
drm_atomic_helper_shutdown() by seeing if drvdata is non-NULL.

Suggested-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230901164111.RFT.3.Iea742f06d8bec41598aa40378fc625fbd7e8a3d6@changeid