spl: Kconfig: Replace CONFIG_SPL_FAT_SUPPORT with CONFIG_SPL_FS_FAT

Replace CONFIG_SPL_FAT_SUPPORT with CONFIG_SPL_FS_FAT so
obj-$(CONFIG_$(SPL_)FS_FAT) 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: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/doc/README.SPL b/doc/README.SPL
index fc1ca1a..48981bd 100644
--- a/doc/README.SPL
+++ b/doc/README.SPL
@@ -53,7 +53,7 @@
 CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o)
 CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o)
 CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o)
-CONFIG_SPL_FAT_SUPPORT (fs/fat/libfat.o)
+CONFIG_SPL_FS_FAT (fs/fat/libfat.o)
 CONFIG_SPL_EXT_SUPPORT
 CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o)
 CONFIG_SPL_POWER_SUPPORT (drivers/power/libpower.o)