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/include/hwconfig.h b/include/hwconfig.h
index a037ed8..def7ad0 100644
--- a/include/hwconfig.h
+++ b/include/hwconfig.h
@@ -6,10 +6,7 @@
  *
  * Author: Anton Vorontsov <avorontsov@ru.mvista.com>
  *
- * 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+
  */
 
 #ifndef _HWCONFIG_H