microblaze/of: Use generic rule to build dtb's

Modify arch/powerpc/boot/Makefile to use dtc command in
scripts/Makefile.lib
Signed-off-by: NDirk Brandewie <dirk.brandewie@gmail.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>

arch/microblaze/boot/Makefile

@@ -10,9 +10,6 @@ targets := linux.bin linux.bin.gz simpleImage.%
 
 OBJCOPYFLAGS := -O binary
 
-# Where the DTS files live
-dtstree         := $(srctree)/$(src)/dts
-
 # Ensure system.dtb exists
 $(obj)/linked_dtb.o: $(obj)/system.dtb
 
@@ -51,14 +48,11 @@ $(obj)/simpleImage.%: vmlinux FORCE
 	$(call if_changed,strip)
 	@echo 'Kernel: $@ is ready' ' (#'`cat .version`')'
 
-# Rule to build device tree blobs
-DTC = $(objtree)/scripts/dtc/dtc
 
 # Rule to build device tree blobs
-quiet_cmd_dtc = DTC     $@
-	cmd_dtc = $(DTC) -O dtb -o $(obj)/$*.dtb -b 0 -p 1024 $(dtstree)/$*.dts
+DTC_FLAGS := -p 1024
 
-$(obj)/%.dtb: $(dtstree)/%.dts FORCE
-	$(call if_changed,dtc)
+$(obj)/%.dtb: $(src)/dts/%.dts FORCE
+	$(call cmd,dtc)
 
 clean-files += *.dtb simpleImage.*.unstrip linux.bin.ub