fanotify: Select EXPORTFS

Fanotify now uses exportfs_encode_inode_fh() so it needs to select
EXPORTFS.

Fixes: e9e0c890 "fanotify: encode file identifier for FAN_REPORT_FID"
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jan Kara <jack@suse.cz>