dm: core: Add livetree address functions

Add functions to access addresses in the device tree. These are brought
in from Linux 4.10.

Also fix up the header guard for fdtaddr.h to avoid confusion.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/dm/fdtaddr.h

@@ -8,8 +8,8 @@
  * SPDX-License-Identifier:	GPL-2.0+
  */
 
-#ifndef _DM_ADDR_H
-#define _DM_ADDR_H
+#ifndef _DM_FDTADDR_H
+#define _DM_FDTADDR_H
 
 #include <fdtdec.h>