m68k: set ColdFire MMU page size

We use the ColdFire V4e MMU page size of 8KiB. Define PAGE_SHIFT
appropriately.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Matt Waddel <mwaddel@yahoo.com>
Acked-by: Kurt Mahan <kmahan@xmission.com>