dtb: add precompile before make dtb.

Change-Id: I91de0c8b0a1e0fbb64ab9e1e3fc52814bac290b9
Signed-off-by: QiaoChong <qiaochong@loongson.cn>

zloader/Makefile.inc

@@ -143,7 +143,8 @@ gencode=./genram
 endif
 
 dtb:
-	./dtc -I dts -O dtb -o ${TARGET}.dtb ../Targets/${TARGET}/conf/${TARGET}.dts
+	gcc    -E  -nostdinc  -D__ASSEMBLY__ -undef -D__DTS__ -x assembler-with-cpp  -o ${TARGET}.dtb.i ../Targets/${TARGET}/conf/${TARGET}.dts
+	./dtc -I dts -O dtb -o ${TARGET}.dtb  ${TARGET}.dtb.i
 	[ -f gzrom.bin ] && cp gzrom.bin gzrom-dtb.bin && python ../tools/pmonenv.py -f gzrom-dtb.bin -d ${TARGET}.dtb -w  al=\(usb0,0\)/boot/vmlinuz al1=\(wd0,0\)/boot/vmlinuz append="'console=ttyS0,115200 console=tty initcall_debug=1 loglevel=20'" FR=1
 cleanall: clean
 	make -C ../Targets/${TARGET}/compile/${TARGETEL}/ clean