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/lib/rbtree.c b/lib/rbtree.c
index 42eab49..b05f1ab 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -3,19 +3,7 @@
   (C) 1999  Andrea Arcangeli <andrea@suse.de>
   (C) 2002  David Woodhouse <dwmw2@infradead.org>
 
-  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.
-
-  This program is distributed in the hope that it will be useful,
-  but WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-  GNU General Public License for more details.
-
-  You should have received a copy of the GNU General Public License
-  along with this program; if not, write to the Free Software
-  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ * SPDX-License-Identifier:	GPL-2.0+
 
   linux/lib/rbtree.c
 */