tools: use files from scripts/dtc/libfdt where possible

Prior to this commit, tools/Makefile pulls all libfdt files from
lib/libfdt.

lib/libfdt/ and scripts/dtc/libfdt have the same copies for the
followings 6 files:
  fdt.c fdt_addresses.c fdt_empty_tree.c fdt_overlay.c fdt_strerr.c
  fdt_sw.c

This commit changes them to #include ones from scripts/dtc/libfdt.

Unfortunately, U-Boot locally modified the following 3 files:
  fdt_ro.c fdt_wip.c fdt_rw.c

I did not touch them in order to avoid unpredictable impact.

The fdt_region.c is U-Boot own file.  This is also borrowed from
lib/libfdt/.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/tools/Makefile b/tools/Makefile
index 2b87e18..acbcd87 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -58,12 +58,17 @@
 hostprogs-$(CONFIG_FIT_SIGNATURE) += fit_info fit_check_sign
 
 FIT_SIG_OBJS-$(CONFIG_FIT_SIGNATURE) := common/image-sig.o
-# Flattened device tree objects
-LIBFDT_CSRCS := fdt.c fdt_ro.c fdt_wip.c fdt_sw.c fdt_rw.c fdt_strerror.c  \
-			fdt_empty_tree.c fdt_addresses.c fdt_overlay.c \
-			fdt_region.c
+
+# The following files are synced with upstream DTC.
+# Use synced versions from scripts/dtc/libfdt/.
+LIBFDT_SRCS_SYNCED := fdt.c fdt_sw.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_wip.c fdt_rw.c fdt_region.c
 
-LIBFDT_OBJS := $(addprefix lib/libfdt/, $(patsubst %.c, %.o, $(LIBFDT_CSRCS)))
+LIBFDT_OBJS := $(addprefix libfdt/, $(patsubst %.c, %.o, $(LIBFDT_SRCS_SYNCED))) \
+	       $(addprefix lib/libfdt/, $(patsubst %.c, %.o, $(LIBFDT_SRCS_UNSYNCED)))
 
 RSA_OBJS-$(CONFIG_FIT_SIGNATURE) := $(addprefix lib/rsa/, \
 					rsa-sign.o rsa-verify.o rsa-checksum.o \