m68knommu: Move __flush_cache_all definition for m54xx in m54xxacr.h

__flush_cache_all for m54xx is intrinsically related to the bit
definitions in m54xxacr.h.  Move it there from cacheflush_no.h,
for easier maintenance.

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