spl: Kconfig: Replace CONFIG_SPL_EXT_SUPPORT to CONFIG_SPL_FS_EXT4

Replace CONFIG_SPL_EXT_SUPPORT to CONFIG_SPLY_FS_EXT4 so both
obj-$(CONFIG_$(SPL_)FS_EXT4) and CONFIG_IS_ENABLED(FS_EXT4) can be
used to control the build in both SPL and U-Boot.

Signed-off-by: Tien Fong Chee <tien.fong.chee@intel.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/include/configs/socfpga_common.h b/include/configs/socfpga_common.h
index be6750a..ea992fa 100644
--- a/include/configs/socfpga_common.h
+++ b/include/configs/socfpga_common.h
@@ -266,7 +266,7 @@
 
 /* SPL SDMMC boot support */
 #ifdef CONFIG_SPL_MMC_SUPPORT
-#if defined(CONFIG_SPL_FS_FAT) || defined(CONFIG_SPL_EXT_SUPPORT)
+#if defined(CONFIG_SPL_FS_FAT) || defined(CONFIG_SPL_FS_EXT4)
 #define CONFIG_SPL_FS_LOAD_PAYLOAD_NAME		"u-boot-dtb.img"
 #define CONFIG_SYS_MMCSD_FS_BOOT_PARTITION	1
 #endif