m68k: export m68k_mmutype

UIO needs m68k_mmutype:

ERROR: "m68k_mmutype" [drivers/uio/uio.ko] undefined!

(noticed by Christian T. Steigies)

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>