m68knommu: create optimal separate instruction and data cache for ColdFire

Create separate functions to deal with instruction and data cache flushing.
This way we can optimize them for the vairous cache types and arrangements
used across the ColdFire family.

For example the unified caches in the version 3 cores means we don't
need to flush the instruction cache. For the version 2 cores that do
not do data cacheing (or where we choose instruction cache only) we
don't need to do any data flushing.

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