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/common/spl/Makefile b/common/spl/Makefile
index 0569d7e..e1daabf 100644
--- a/common/spl/Makefile
+++ b/common/spl/Makefile
@@ -24,7 +24,7 @@
 obj-$(CONFIG_$(SPL_TPL_)OPTEE) += spl_optee.o
 obj-$(CONFIG_$(SPL_TPL_)USB_SUPPORT) += spl_usb.o
 obj-$(CONFIG_$(SPL_TPL_)FS_FAT) += spl_fat.o
-obj-$(CONFIG_$(SPL_TPL_)EXT_SUPPORT) += spl_ext.o
+obj-$(CONFIG_$(SPL_TPL_)FS_EXT4) += spl_ext.o
 obj-$(CONFIG_$(SPL_TPL_)SATA_SUPPORT) += spl_sata.o
 obj-$(CONFIG_$(SPL_TPL_)DFU) += spl_dfu.o
 obj-$(CONFIG_$(SPL_TPL_)SPI_LOAD) += spl_spi.o