libfdt: migrate fdt_ro.c to a wrapper of scripts/dtc/libfdt/fdt_ro.c

There is no essential difference between scripts/dtc/libfdt/fdt_ro.c
and lib/libfdt/fdt_ro.c

Migrate to a simple wrapper like the other files.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
diff --git a/lib/libfdt/Makefile b/lib/libfdt/Makefile
index 5d3ae4e..878659f 100644
--- a/lib/libfdt/Makefile
+++ b/lib/libfdt/Makefile
@@ -3,9 +3,9 @@
 # (C) Copyright 2000-2007
 # Wolfgang Denk, DENX Software Engineering, wd@denx.de.
 
-# Use upstream code.
 obj-y += \
 	fdt.o \
+	fdt_ro.o \
 	fdt_wip.o \
 	fdt_strerror.o \
 	fdt_sw.o \
@@ -15,10 +15,6 @@
 
 obj-$(CONFIG_OF_LIBFDT_OVERLAY) += fdt_overlay.o
 
-# Locally modified for U-Boot.
-# TODO: split out the local modifiction.
-obj-y += fdt_ro.o
-
 # U-Boot own file
 obj-y += fdt_region.o