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/lib/lmb.c b/lib/lmb.c
index c5e75fb..081e418 100644
--- a/lib/lmb.c
+++ b/lib/lmb.c
@@ -4,10 +4,7 @@
  * Peter Bergner, IBM Corp.	June 2001.
  * Copyright (C) 2001 Peter Bergner.
  *
- *      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+
  */
 
 #include <common.h>