drm/imx: Use __drm_atomic_helper_plane_reset instead of copying the logic

A new helper function(__drm_atomic_helper_plane_reset) has been added
for linking a plane with its state and resetting the core
properties(alpha, rotation, etc.) to their default values.
Use that instead of duplicating the logic.
Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20180804161530.12275-7-alexandru-cosmin.gheorghe@arm.com

drivers/gpu/drm/imx/ipuv3-plane.c

@@ -281,16 +281,13 @@ static void ipu_plane_state_reset(struct drm_plane *plane)
 		ipu_state = to_ipu_plane_state(plane->state);
 		__drm_atomic_helper_plane_destroy_state(plane->state);
 		kfree(ipu_state);
+		plane->state = NULL;
 	}
 
 	ipu_state = kzalloc(sizeof(*ipu_state), GFP_KERNEL);
 
-	if (ipu_state) {
-		ipu_state->base.plane = plane;
-		ipu_state->base.rotation = DRM_MODE_ROTATE_0;
-	}
-
-	plane->state = &ipu_state->base;
+	if (ipu_state)
+		__drm_atomic_helper_plane_reset(plane, &ipu_state->base);
 }
 
 static struct drm_plane_state *