drm/tegra: 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.
Suggested-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240612152336.v2.3.Ifb4450979b62976fd5a98847dade2e5b377d47c8@changeid

drivers/gpu/drm/tegra/drm.c

@@ -1330,6 +1330,11 @@ static int host1x_drm_remove(struct host1x_device *dev)
 	return 0;
 }
 
+static void host1x_drm_shutdown(struct host1x_device *dev)
+{
+	drm_atomic_helper_shutdown(dev_get_drvdata(&dev->dev));
+}
+
 #ifdef CONFIG_PM_SLEEP
 static int host1x_drm_suspend(struct device *dev)
 {
@@ -1398,6 +1403,7 @@ static struct host1x_driver host1x_drm_driver = {
 	},
 	.probe = host1x_drm_probe,
 	.remove = host1x_drm_remove,
+	.shutdown = host1x_drm_shutdown,
 	.subdevs = host1x_drm_subdevs,
 };