Revert "kbuild: remove unused dtc-version.sh script"

We need this to make building dtc optional. It makes no sense to build our
own dtc if the system one works correctly.

This reverts commit ddb87a0b40262ff99d675e946f57427642303938.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index 71f468c..8845c6f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -756,6 +756,7 @@
 F:	include/linux/libfdt*
 F:	cmd/fdt.c
 F:	common/fdt_support.c
+F:	scripts/dtc-version.sh
 
 FREEBSD
 M:	Rafal Jaworowski <raj@semihalf.com>