libfdt: Export overlay_apply_node() as fdt_overlay_apply_node()

This function is useful to merge a subset of DT into another DT, for
example if some prior-stage firmware passes a DT fragment to U-Boot
and U-Boot needs to merge it into its own DT. Export this function
to permit implementing such functionality.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
diff --git a/scripts/dtc/libfdt/fdt_overlay.c b/scripts/dtc/libfdt/fdt_overlay.c
index be71873..c090e69 100644
--- a/scripts/dtc/libfdt/fdt_overlay.c
+++ b/scripts/dtc/libfdt/fdt_overlay.c
@@ -879,3 +879,8 @@
 
 	return ret;
 }
+
+int fdt_overlay_apply_node(void *fdt, int target, void *fdto, int node)
+{
+	return overlay_apply_node(fdt, target, fdto, node);
+}