staging: exfat: make exfat depend on BLOCK

This should fix a build error in some configurations when CONFIG_BLOCK
is not selected.  Also properly set the dependancy for no FAT support at
the same time.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Link: https://lore.kernel.org/r/20190902174631.GB31445@kroah.com


Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>