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/scripts/Kbuild.include b/scripts/Kbuild.include
index a745cc4..09506cb 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -148,6 +148,7 @@
 
 # added for U-Boot
 binutils-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/binutils-version.sh $(AS))
+dtc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/dtc-version.sh $(DTC))
 
 # cc-ldoption
 # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)