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/zc5202_defconfig b/configs/zc5202_defconfig
index f0b51b6..cca1f2d 100644
--- a/configs/zc5202_defconfig
+++ b/configs/zc5202_defconfig
@@ -19,7 +19,7 @@
 CONFIG_DEFAULT_FDT_FILE="imx6q-zc5202.dtb"
 CONFIG_BOUNCE_BUFFER=y
 CONFIG_BOARD_EARLY_INIT_F=y
-CONFIG_SPL_EXT_SUPPORT=y
+CONFIG_SPL_FS_EXT4=y
 CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_SPL_SPI_LOAD=y
 CONFIG_SPL_WATCHDOG_SUPPORT=y