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/net/nfs.h b/net/nfs.h
index a5a1b43..53451db 100644
--- a/net/nfs.h
+++ b/net/nfs.h
@@ -1,10 +1,7 @@
 /*
  * (C) Masami Komiya <mkomiya@sonare.it> 2004
  *
- * 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, or (at
- * your option) any later version.
+ * SPDX-License-Identifier:	GPL-2.0+
  */
 
 #ifndef __NFS_H__