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/configs/cm_t43_defconfig b/configs/cm_t43_defconfig
index 817798a..fe548f2 100644
--- a/configs/cm_t43_defconfig
+++ b/configs/cm_t43_defconfig
@@ -19,7 +19,7 @@
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0x480
-CONFIG_SPL_EXT_SUPPORT=y
+CONFIG_SPL_FS_EXT4=y
 CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_SPL_MTD_SUPPORT=y
 # CONFIG_SPL_NAND_SUPPORT is not set