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/lib/_ashrdi3.S b/arch/powerpc/lib/_ashrdi3.S
index f28ab49..6209166 100644
--- a/arch/powerpc/lib/_ashrdi3.S
+++ b/arch/powerpc/lib/_ashrdi3.S
@@ -8,10 +8,7 @@
  * 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 <ppc_asm.tmpl>