Add GPL-2.0+ SPDX-License-Identifier to source files

Signed-off-by: Wolfgang Denk <wd@denx.de>
[trini: Fixup common/cmd_io.c]
Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/board/sixnet/sixnet.c b/board/sixnet/sixnet.c
index a13c72d..06b2083 100644
--- a/board/sixnet/sixnet.c
+++ b/board/sixnet/sixnet.c
@@ -3,23 +3,9 @@
  * Dave Ellis, SIXNET, dge@sixnetio.com.
  *  Based on code by:
  * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
- * and other contributors to U-Boot. See file CREDITS for list
- * of people who contributed to this  project.
+ * and other contributors to U-Boot.
  *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License as
- * published by the Free Software Foundation; either version 2 of
- * the License, or (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
- * MA 02111-1307 USA
+ * SPDX-License-Identifier:	GPL-2.0+
  */
 
 #include <common.h>