dtc: Switch to building and using our own dtc unless provided

This makes us act like the Linux Kernel does and allow for dtc to be
provided externally but otherwise we use the version of dtc that is
included in the sources.  This in turn means that we can drop the
checkdtc logic.  We select DTC in the cases where we will need the dtc
tool provided.

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

Makefile

@@ -349,7 +349,7 @@ OBJDUMP		= $(CROSS_COMPILE)objdump
 AWK		= awk
 PERL		= perl
 PYTHON		?= python
-DTC		?= dtc
+DTC		?= $(objtree)/scripts/dtc/dtc
 CHECK		= sparse
 
 CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
@@ -872,7 +872,7 @@ endif
 PHONY += dtbs
 dtbs: dts/dt.dtb
 	@:
-dts/dt.dtb: checkdtc u-boot
+dts/dt.dtb: u-boot
 	$(Q)$(MAKE) $(build)=dts dtbs
 
 quiet_cmd_copy = COPY    $@
@@ -1447,12 +1447,6 @@ SYSTEM_MAP = \
 System.map:	u-boot
 		@$(call SYSTEM_MAP,$<) > $@
 
-checkdtc:
-	@if test $(call dtc-version) -lt 010403; then \
-		echo '*** Your dtc is too old, please upgrade to dtc 1.4.3 or newer'; \
-		false; \
-	fi
-
 #########################################################################
 
 # ARM relocations should all be R_ARM_RELATIVE (32-bit) or