m68knommu: hard set the ColdFire MBAR register on startup

The ColdFire MBAR register that holds the mapping of the peripheral region
on some ColdFire CPUs is configurable. It can be configured at some address
different to that of the bootloader that loaded the kernel. So hard set
the MBAR register mapping at kernel startup time.

Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>