To check current running kernel file system type support you can
root@debian:~# cat /proc/filesystems
the output show what is currently kernel supported file system type.
Logically speaking if mount
report unknown filesystem type, You option are limit to make the file system type available to kernel unless it is unsupported type for your running kernel. you can use the command
root@debian:~# modprobe vfat
to load the kernel module. if the kernel module is not available then your options is get a newer kernel with build in vfat
module or have matching modules load in you /lib/modules/`uname -r`/