imx: imx8mq: build flash.bin

Build flash.bin for i.MX8MQ, it will include signed hdmi firmware,
spl, ddr firmware, fit image(bl31.bin, u-boot-nodtb.bin, dtb).
Burn it to 33KB offset of SD card.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/Makefile b/Makefile
index 19d7343..fe41a5f 100644
--- a/Makefile
+++ b/Makefile
@@ -1208,6 +1208,11 @@
 SPL: spl/u-boot-spl.bin FORCE
 	$(Q)$(MAKE) $(build)=arch/arm/mach-imx $@
 
+ifeq ($(CONFIG_ARCH_IMX8M), y)
+flash.bin: spl/u-boot-spl.bin u-boot.itb FORCE
+	$(Q)$(MAKE) $(build)=arch/arm/mach-imx $@
+endif
+
 u-boot-with-spl.imx u-boot-with-nand-spl.imx: SPL u-boot.bin FORCE
 	$(Q)$(MAKE) $(build)=arch/arm/mach-imx $@