Validate dtc is new enough

Subsequent patches assume that dtc supports various recent features.
These are available in dtc 1.4.0. Validate that dtc is at least that
version.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/Makefile b/Makefile
index 7206aba..d545d30 100644
--- a/Makefile
+++ b/Makefile
@@ -413,7 +413,7 @@
 
 all:		$(ALL-y) $(SUBDIR_EXAMPLES)
 
-$(obj)u-boot.dtb:	$(obj)u-boot
+$(obj)u-boot.dtb:	checkdtc $(obj)u-boot
 		$(MAKE) -C dts binary
 		mv $(obj)dts/dt.dtb $@
 
@@ -667,6 +667,12 @@
 		false; \
 	fi
 
+checkdtc:
+	@if test $(call dtc-version) -lt 0104; then \
+		echo '*** Your dtc is too old, please upgrade to dtc 1.4 or newer'; \
+		false; \
+	fi
+
 #
 # Auto-generate the autoconf.mk file (which is included by all makefiles)
 #