fdt: Add support for a separate device tree (CONFIG_OF_SEPARATE)

This adds support for an FDT to be build as a separate binary file called
u-boot.dtb. This can be concatenated with the U-Boot binary to provide a
device tree located at run-time by U-Boot. The Makefile is modified to
provide this file in u-boot-dtb.bin.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/Makefile b/Makefile
index ce81bb0..684cdb6 100644
--- a/Makefile
+++ b/Makefile
@@ -359,9 +359,17 @@
 ONENAND_BIN ?= $(obj)onenand_ipl/onenand-ipl-2k.bin
 ALL-$(CONFIG_MMC_U_BOOT) += $(obj)mmc_spl/u-boot-mmc-spl.bin
 ALL-$(CONFIG_SPL) += $(obj)spl/u-boot-spl.bin
+ALL-$(CONFIG_OF_SEPARATE) += $(obj)u-boot.dtb $(obj)u-boot-dtb.bin
 
 all:		$(ALL-y) $(SUBDIR_EXAMPLES)
 
+$(obj)u-boot.dtb:	$(obj)u-boot
+		$(MAKE) -C dts binary
+		mv $(obj)dts/dt.dtb $@
+
+$(obj)u-boot-dtb.bin:	$(obj)u-boot.bin $(obj)u-boot.dtb
+		cat $^ >$@
+
 $(obj)u-boot.hex:	$(obj)u-boot
 		$(OBJCOPY) ${OBJCFLAGS} -O ihex $< $@