m68knommu: make 523x UART platform addressing consistent

If we make all UART addressing consistent across all ColdFire family members
then we will be able to remove the duplicated plaform data and use a single
setup for all.

So modify the ColdFire 523x UART addressing so that:

. UARTs are numbered from 0 up
. use a common name for IRQs used

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