Makefile: socfpga: Add target to generate hex output for combined spl and dtb

Add target to Makefile to generate "u-boot-spl-dtb.hex" for Intel
SOCFPGA SOC64 devices (Stratix 10 and Agilex). "u-boot-spl-dtb.hex"
is hex formatted spl with and offset of CONFIG_SPL_TEXT_BASE. It
combines the spl image and dtb. "u-boot-spl-dtb.hex" is needed to
generate the final configuration bitstream for Intel SOCFPGA SOC64
devices.

Signed-off-by: Dalon Westergreen <dalon.westergreen@intel.com>
Signed-off-by: Siew Chin Lim <elly.siew.chin.lim@intel.com>
diff --git a/scripts/Makefile.spl b/scripts/Makefile.spl
index ea4e045..1fd63ef 100644
--- a/scripts/Makefile.spl
+++ b/scripts/Makefile.spl
@@ -229,6 +229,8 @@
 INPUTS-y	+= $(obj)/$(SPL_BIN).sfp
 endif
 
+INPUTS-$(CONFIG_TARGET_SOCFPGA_SOC64) += $(obj)/u-boot-spl-dtb.hex
+
 ifdef CONFIG_ARCH_SUNXI
 INPUTS-y	+= $(obj)/sunxi-spl.bin
 
@@ -389,6 +391,11 @@
 MKIMAGEFLAGS_sunxi-spl.bin = -T sunxi_egon \
 	-n $(CONFIG_DEFAULT_DEVICE_TREE)
 
+OBJCOPYFLAGS_u-boot-spl-dtb.hex := -I binary -O ihex --change-address=$(CONFIG_SPL_TEXT_BASE)
+
+$(obj)/u-boot-spl-dtb.hex: $(obj)/u-boot-spl-dtb.bin FORCE
+	$(call if_changed,objcopy)
+
 $(obj)/sunxi-spl.bin: $(obj)/$(SPL_BIN).bin FORCE
 	$(call if_changed,mkimage)