common: Move device-tree setup functions to fdt_support.h

These functions relate to setting up the device tree for booting the OS.
The fdt_support.h header file supports similar functions, so move these
there.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/hisilicon/hikey/hikey.c b/board/hisilicon/hikey/hikey.c
index 940ae82..28f5cf7 100644
--- a/board/hisilicon/hikey/hikey.c
+++ b/board/hisilicon/hikey/hikey.c
@@ -5,6 +5,7 @@
  */
 #include <common.h>
 #include <dm.h>
+#include <fdt_support.h>
 #include <dm/platform_data/serial_pl01x.h>
 #include <errno.h>
 #include <malloc.h>