fs: fat: add kbuild configuration support

Add Kconfig symbols for various configurations
supported by FAT filesystem support code.

CONFIG_SUPPORT_VFAT has been left out since its
force enabled in include/fat.h and probably
should get removed at some point.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
[trini: add select FS_FAT for CMD_FAT and SPL_FAT_SUPPORT]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 6f75b86..270cff6 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1166,6 +1166,7 @@
 
 config CMD_FAT
 	bool "FAT command support"
+	select FS_FAT
 	help
 	  Support for the FAT fs