ARM: socfpga: Build sfp image only for Gen5 and Arria10 devices

The sfp file is only valid for Gen5 (Cyclone5 & Arria5) and Arria10
devices.  The file should only be built for these devices.

Signed-off-by: Dalon Westergreen <dalon.westergreen@intel.com>
diff --git a/Kconfig b/Kconfig
index 512c7be..305b265 100644
--- a/Kconfig
+++ b/Kconfig
@@ -226,7 +226,8 @@
 
 config BUILD_TARGET
 	string "Build target special images"
-	default "u-boot-with-spl.sfp" if ARCH_SOCFPGA
+	default "u-boot-with-spl.sfp" if TARGET_SOCFPGA_ARRIA10
+	default "u-boot-with-spl.sfp" if TARGET_SOCFPGA_GEN5
 	default "u-boot-spl.kwb" if ARCH_MVEBU && SPL
 	default "u-boot-elf.srec" if RCAR_GEN3
 	default "u-boot.itb" if SPL_LOAD_FIT && ARCH_SUNXI