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/freescale/mx6slevk/imximage.cfg b/board/freescale/mx6slevk/imximage.cfg
index df39a16..16ea597 100644
--- a/board/freescale/mx6slevk/imximage.cfg
+++ b/board/freescale/mx6slevk/imximage.cfg
@@ -1,10 +1,7 @@
 /*
  * Copyright (C) 2013 Freescale Semiconductor, Inc.
  *
- * 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.
+ * SPDX-License-Identifier:	GPL-2.0+
  *
  * Refer docs/README.imxmage for more details about how-to configure
  * and create imximage boot image