drm: rcar-du: Let core take care of normalizing the zpos

Set the drm_mode_config->normalize_zpos and call drm_atomic_helper_check()
from rcar_du_atomic_check() instead of re implementing the function locally.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
CC: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180321102029.15248-6-peter.ujfalusi@ti.com

drivers/gpu/drm/rcar-du/rcar_du_kms.c

@@ -233,15 +233,7 @@ static int rcar_du_atomic_check(struct drm_device *dev,
 	struct rcar_du_device *rcdu = dev->dev_private;
 	int ret;
 
-	ret = drm_atomic_helper_check_modeset(dev, state);
-	if (ret)
-		return ret;
-
-	ret = drm_atomic_normalize_zpos(dev, state);
-	if (ret)
-		return ret;
-
-	ret = drm_atomic_helper_check_planes(dev, state);
+	ret = drm_atomic_helper_check(dev, state);
 	if (ret)
 		return ret;
 
@@ -529,6 +521,7 @@ int rcar_du_modeset_init(struct rcar_du_device *rcdu)
 	dev->mode_config.min_height = 0;
 	dev->mode_config.max_width = 4095;
 	dev->mode_config.max_height = 2047;
+	dev->mode_config.normalize_zpos = true;
 	dev->mode_config.funcs = &rcar_du_mode_config_funcs;
 	dev->mode_config.helper_private = &rcar_du_mode_config_helper;