feat(st): mandate dtc version 1.4.7

To be able to use /omit-if-no-ref/ in DT files, the dtc version should
be at least 1.4.7. Update the makefile rule that checks dtc version.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I06bde289cf359a7383694e4c86991dfba781e7d7
diff --git a/plat/st/common/common_rules.mk b/plat/st/common/common_rules.mk
index 302624e..fa48dfc 100644
--- a/plat/st/common/common_rules.mk
+++ b/plat/st/common/common_rules.mk
@@ -35,8 +35,8 @@
 	${Q}${MAKE} --no-print-directory -C ${STM32IMAGEPATH} clean
 
 check_dtc_version:
-	@if [ ${DTC_VERSION} -lt 10404 ]; then \
-		echo "dtc version too old (${DTC_V}), you need at least version 1.4.4"; \
+	@if [ ${DTC_VERSION} -lt 10407 ]; then \
+		echo "dtc version too old (${DTC_V}), you need at least version 1.4.7"; \
 		false; \
 	fi