drm/rockchip: support atomic asynchronous commit

If drm core requests a async commit, rockchip_drm_atomic_commit
will schedule a work task to update later.

Signed-off-by: Mark Yao <mark.yao@rock-chips.com>
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
index 929eb30..8397d1b 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
@@ -140,6 +140,9 @@
 	if (!private)
 		return -ENOMEM;
 
+	mutex_init(&private->commit.lock);
+	INIT_WORK(&private->commit.work, rockchip_drm_atomic_work);
+
 	drm_dev->dev_private = private;
 
 	drm_mode_config_init(drm_dev);