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/freescale/ls1021atsn/ls1021atsn.c b/board/freescale/ls1021atsn/ls1021atsn.c
index 8039fd5..532ca89 100644
--- a/board/freescale/ls1021atsn/ls1021atsn.c
+++ b/board/freescale/ls1021atsn/ls1021atsn.c
@@ -2,6 +2,7 @@
 /* Copyright 2016-2019 NXP Semiconductors
  */
 #include <common.h>
+#include <fdt_support.h>
 #include <init.h>
 #include <asm/arch-ls102xa/ls102xa_soc.h>
 #include <asm/arch/ls102xa_devdis.h>