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

The only difference between scripts/dtc/libfdt/fdt_rw.c and
lib/libfdt/fdt_rw.c is fdt_remove_unused_strings().

It is only used by fdtgrep, so we do not need to compile it for U-Boot
image.  Move it to tools/libfdt/fdw_rw.c so that lib/libfdt/fdt_rw.c
can be a wrapper of scripts/dtc/libfdt/fdt_rw.c.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/Makefile b/tools/Makefile
index b7d7d41..f8731e7 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -63,11 +63,11 @@
 
 # The following files are synced with upstream DTC.
 # Use synced versions from scripts/dtc/libfdt/.
-LIBFDT_SRCS_SYNCED := fdt.c fdt_wip.c fdt_sw.c fdt_strerror.c fdt_empty_tree.c \
-		      fdt_addresses.c fdt_overlay.c
+LIBFDT_SRCS_SYNCED := fdt.c fdt_wip.c fdt_sw.c fdt_rw.c \
+		fdt_strerror.c fdt_empty_tree.c fdt_addresses.c fdt_overlay.c
 # The following files are locally modified for U-Boot (unfotunately).
 # Use U-Boot own versions from lib/libfdt/.
-LIBFDT_SRCS_UNSYNCED := fdt_ro.c fdt_rw.c fdt_region.c
+LIBFDT_SRCS_UNSYNCED := fdt_ro.c fdt_region.c
 
 LIBFDT_OBJS := $(addprefix libfdt/, $(patsubst %.c, %.o, $(LIBFDT_SRCS_SYNCED))) \
 	       $(addprefix lib/libfdt/, $(patsubst %.c, %.o, $(LIBFDT_SRCS_UNSYNCED)))