m68knommu: fix 528x ColdFire cache settings

Fix problems with the 528x ColdFire CPU cache setup.
Do not cache the flash region (if present), and make the runtime
settings consistent with the init setting.

Problems pointed out by Bernd Buttner <b.buettner@mkc-gmbh.de>

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>