m68knommu: remove address offsets relative to IPSBAR for ColdFire 527x

Remove the last address definitions relative to the IPSBAR peripheral region
for the ColdFire 527x family. This involved cleaning up some magic numbers
used in the code part, and making them proper register definitions in the 527x
specific header.

This is part of the process of cleaning up the ColdFire register definitions
to make them consistently use absolute addresses for the primary registers.
This will reduce the occasional bugs caused by inconsistent definition of
the register addresses.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>