m68knommu: fix DMA support for ColdFire

ColdFire CPU family members support DMA (all those with the FEC ethernet
core use it, the rest have dedicated DMA engines). The code support is
just missing a handful of routines for it to be usable by drivers.
Add the missing dma_ functions.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>