kernel: Add missing MODULE_VERSION()s for file systems.

kernel: Add missing MODULE_VERSION()s for file systems.

The loader will figure out by itself whether to load a module or not,
depending on whether it's already in the kernel config or not, iif
MODULE_VERSION() is present.

I.e., if MSDOSFS (that has MODULE_VERSION()) is in the config and
msdos_load="YES" is in /boot/loader.conf, msdos.ko will not be loaded
by the loader at all.

Without MODULE_VERSION() it will lead (in the best case) to whining in
dmesg like for ahci or (in the worst case) to weird behavior, such as
for nullfs:

# mount -a
null: vfsload(null): No such file or directory

Therefore, we definitely want MODULE_VERSION() for all new modules.

This commit is the first in a series to add the missing MODULE_VERSION()s.

I know that ufs is not a module, just included it for completeness' sake.

Reported-by: marino, tuxillo