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/arch/powerpc/cpu/ppc4xx/cache.S b/arch/powerpc/cpu/ppc4xx/cache.S
index 757d7da..2714c2f 100644
--- a/arch/powerpc/cpu/ppc4xx/cache.S
+++ b/arch/powerpc/cpu/ppc4xx/cache.S
@@ -5,11 +5,7 @@
  * Largely rewritten by Cort Dougan (cort@cs.nmt.edu)
  * and Paul Mackerras.
  *
- * 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 <config.h>