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/riotboard_spl_defconfig b/configs/riotboard_spl_defconfig
index 8213469..2298d5b 100644
--- a/configs/riotboard_spl_defconfig
+++ b/configs/riotboard_spl_defconfig
@@ -18,7 +18,7 @@
 CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE=y
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL_RAW_IMAGE_SUPPORT=y
-CONFIG_SPL_EXT_SUPPORT=y
+CONFIG_SPL_FS_EXT4=y
 CONFIG_SPL_OS_BOOT=y
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_GPIO=y