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/Kconfig b/common/spl/Kconfig
index eac50ac..5902852 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -387,7 +387,7 @@
 	  is required since the network stack uses a number of environment
 	  variables. See also SPL_NET_SUPPORT.
 
-config SPL_EXT_SUPPORT
+config SPL_FS_EXT4
 	bool "Support EXT filesystems"
 	help
 	  Enable support for EXT2/3/4 filesystems with SPL. This permits