m68knommu: Create new m54xxacr.h from m5407sim.h subpart

The MCF548x have the same cache control registers as the MCF5407.
Extract the bit definitions for the ACR and CACR registers from m5407sim.h
and move them to a new file m54xxacr.h.  Those definitions are not used
anywhere yet, so no other file is involved.  This is a preparation for
m54xx cache support cleanup.

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>