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/mips/include/asm/u-boot-mips.h b/arch/mips/include/asm/u-boot-mips.h
index e77636e..9f3cce9 100644
--- a/arch/mips/include/asm/u-boot-mips.h
+++ b/arch/mips/include/asm/u-boot-mips.h
@@ -1,6 +1,5 @@
 /*
- * This file is released under the terms of GPL v2 and any later version.
- * See the file COPYING in the root directory of the source tree for details.
+ * SPDX-License-Identifier:	GPL-2.0+
  *
  * Copyright (C) 2003 Wolfgang Denk, DENX Software Engineering, wd@denx.de
  */