scripts/dtc: Update to upstream version v1.4.3

Using the update-dtc-source.sh script from Linux v4.14-rc1 import the
portions of dtc that we require.  We bring in update-dtc-source.sh and
scripts/dtc/Makefile from Linux v4.14-rc1.  Rework DTC_FLAGS handling to
not require a test.

Signed-off-by: Tom Rini <trini@konsulko.com>

scripts/dtc/Makefile.dtc

@@ -0,0 +1,18 @@
+# Makefile.dtc
+#
+# This is not a complete Makefile of itself.  Instead, it is designed to
+# be easily embeddable into other systems of Makefiles.
+#
+DTC_SRCS = \
+	checks.c \
+	data.c \
+	dtc.c \
+	flattree.c \
+	fstree.c \
+	livetree.c \
+	srcpos.c \
+	treesource.c \
+	util.c
+
+DTC_GEN_SRCS = dtc-lexer.lex.c dtc-parser.tab.c
+DTC_OBJS = $(DTC_SRCS:%.c=%.o) $(DTC_GEN_SRCS:%.c=%.o)