Makefile: Add `all` target to MAKE_DTBS

This patch makes some minor changes to `MAKE_DTBS` make macro
and adds `dtbs` target to the `all` make target.

Change-Id: I1c5b4a603ada31d2dac2ed73da9ff707b410dd11
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
diff --git a/Makefile b/Makefile
index 06422ea..87e35e9 100644
--- a/Makefile
+++ b/Makefile
@@ -125,7 +125,7 @@
 OD			:=	${CROSS_COMPILE}objdump
 NM			:=	${CROSS_COMPILE}nm
 PP			:=	${CROSS_COMPILE}gcc -E
-DTC			?=	dtc
+DTC			:=	dtc
 
 # Use ${LD}.bfd instead if it exists (as absolute path or together with $PATH).
 ifneq ($(strip $(wildcard ${LD}.bfd) \
@@ -638,9 +638,7 @@
 
 # Expand build macros for the different images
 ifeq (${NEED_FDT},yes)
-$(eval $(call MAKE_DTBS,$(BUILD_PLAT)/fdts,$(FDT_SOURCES)))
-$(eval $(call MAKE_FDT))
-dtbs: $(DTBS)
+    $(eval $(call MAKE_DTBS,$(BUILD_PLAT)/fdts,$(FDT_SOURCES)))
 endif
 
 locate-checkpatch:
@@ -777,7 +775,7 @@
 	@echo "  distclean      Remove all build artifacts for all platforms"
 	@echo "  certtool       Build the Certificate generation tool"
 	@echo "  fiptool        Build the Firmware Image Package (FIP) creation tool"
-	@echo "  dtbs           Build the Flattened device tree (if required for the platform)"
+	@echo "  dtbs           Build the Device Tree Blobs (if required for the platform)"
 	@echo ""
 	@echo "Note: most build targets require PLAT to be set to a specific platform."
 	@echo ""