This abstracts out all the differences I could see between the netbsd
sparc64 and macppc zs drivers. In particular the offsets of the csr and
data registers are different, so we use a separate bus handle for each and
use bus_space_subregion to add the bus specific offsets.
Requested by: benno
With a 1 byte transmit fifo, 3 byte receive fifo, and wierd multiplexed I/O
designed for a Z80 cpu, this chip redefines suckage.
Based on the openbsd and netbsd drivers. Only really works as a console,
modem support is not complete since I can't test it.
