imx: Add Makefile dependency for mkimage_fit_atf.sh

The mkimage_fit_atf.sh SPL FIT generator script requires
u-boot-nodtb.bin, but this was not enforced by the Makefile. This could
cause the generator script to be executed before u-boot-nodtb.bin has
been created.

Signed-off-by: Chris Spencer <christopher.spencer@sea.co.uk>
Cc: NXP i.MX U-Boot Team <uboot-imx@nxp.com>

Makefile

@@ -1065,7 +1065,10 @@ U_BOOT_ITS = $(subst ",,$(CONFIG_SPL_FIT_SOURCE))
 else
 ifneq ($(CONFIG_SPL_FIT_GENERATOR),"")
 U_BOOT_ITS := u-boot.its
-$(U_BOOT_ITS): FORCE
+ifeq ($(CONFIG_SPL_FIT_GENERATOR),"arch/arm/mach-imx/mkimage_fit_atf.sh")
+U_BOOT_ITS_DEPS += u-boot-nodtb.bin
+endif
+$(U_BOOT_ITS): $(U_BOOT_ITS_DEPS) FORCE
 	$(srctree)/$(CONFIG_SPL_FIT_GENERATOR) \
 	$(patsubst %,arch/$(ARCH)/dts/%.dtb,$(subst ",,$(CONFIG_OF_LIST))) > $@
 endif