m68knommu: make Coldfire 548x support more generic

The ColdFire 547x family of processors is very similar to the ColdFire
548x series. Almost all of the support for them is the same. Make the
code supporting the 548x more gneric, so it will be capable of
supporting both families.

For the most part this is a renaming excerise to make the support
code more obviously apply to both families.

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