gpu: drm: sti: Adopt SPDX identifiers

Add SPDX identifiers to files under sti directory

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Acked-by: Vincent Abriou <vincent.abriou@st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171206112947.9569-2-benjamin.gaignard@st.com

drivers/gpu/drm/sti/sti_plane.h

@@ -1,7 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) STMicroelectronics SA 2014
  * Author: Benjamin Gaignard <benjamin.gaignard@st.com> for STMicroelectronics.
- * License terms:  GNU General Public License (GPL), version 2
  */
 
 #ifndef _STI_PLANE_H_