Use information passed from via the boot arguments to determine which
device to use as the console.
Add support for initialising the CATS ISA subsystem.
During the early bootstrapping use fcomcnattach()/fcomcndetach to enable
debug and diagnostic information to be sent to the diagnostic serial
port. This is only used during the early part of initarm() until things
have been relocated and the real console can be initialised().
