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/include/configs/socfpga_soc64_common.h b/include/configs/socfpga_soc64_common.h
index 0e54601..1cfa190 100644
--- a/include/configs/socfpga_soc64_common.h
+++ b/include/configs/socfpga_soc64_common.h
@@ -194,7 +194,7 @@
  * 0x8000_0000 ...... End of SDRAM_1 (assume 2GB)
  *
  */
-#define CONFIG_SPL_TARGET		"spl/u-boot-spl.hex"
+#define CONFIG_SPL_TARGET		"spl/u-boot-spl-dtb.hex"
 #define CONFIG_SPL_MAX_SIZE		CONFIG_SYS_INIT_RAM_SIZE
 #define CONFIG_SPL_STACK		CONFIG_SYS_INIT_SP_ADDR
 #define CONFIG_SPL_BSS_MAX_SIZE		0x100000	/* 1 MB */