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/arch/arm/mach-socfpga/spl_s10.c b/arch/arm/mach-socfpga/spl_s10.c
index f40a156..a3db20a 100644
--- a/arch/arm/mach-socfpga/spl_s10.c
+++ b/arch/arm/mach-socfpga/spl_s10.c
@@ -33,7 +33,7 @@
 #ifdef CONFIG_SPL_MMC_SUPPORT
 u32 spl_boot_mode(const u32 boot_device)
 {
-#if defined(CONFIG_SPL_FS_FAT) || defined(CONFIG_SPL_EXT_SUPPORT)
+#if defined(CONFIG_SPL_FS_FAT) || defined(CONFIG_SPL_FS_EXT4)
 	return MMCSD_MODE_FS;
 #else
 	return MMCSD_MODE_RAW;