scripts: dtc: Fetch fdtoverlay.c from external DTC project

We will start building overlays for platforms soon in the kernel and
would need fdtoverlay tool going forward. Lets start fetching it.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/28f66f70602225bb6aeb58e924c20bde9d864327.1611904394.git.viresh.kumar@linaro.org

scripts/dtc/update-dtc-source.sh

@@ -37,6 +37,7 @@ DTC_SOURCE="checks.c data.c dtc.c dtc.h flattree.c fstree.c livetree.c srcpos.c
 LIBFDT_SOURCE="fdt.c fdt.h fdt_addresses.c fdt_empty_tree.c \
 		fdt_overlay.c fdt_ro.c fdt_rw.c fdt_strerror.c fdt_sw.c \
 		fdt_wip.c libfdt.h libfdt_env.h libfdt_internal.h"
+FDTOVERLAY_SOURCE=fdtoverlay.c
 
 get_last_dtc_version() {
 	git log --oneline scripts/dtc/ | grep 'upstream' | head -1 | sed -e 's/^.* \(.*\)/\1/'
@@ -54,7 +55,7 @@ dtc_log=$(git log --oneline ${last_dtc_ver}..)
 
 # Copy the files into the Linux tree
 cd $DTC_LINUX_PATH
-for f in $DTC_SOURCE; do
+for f in $DTC_SOURCE $FDTOVERLAY_SOURCE; do
 	cp ${DTC_UPSTREAM_PATH}/${f} ${f}
 	git add ${f}
 done