m68knommu: clean up ColdFire 54xx General Timer definitions

Convert the ColdFire 54xx CPU General Timer register address definitions to
include the MCF_MBAR peripheral region offset. This makes them consistent
with all other 54xx address register definitions (in m54xxsim.h).

The goal is to reduce different definitions used (some including offsets and
others not) causing bugs when used incorrectly.

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