From: Bjorn Helgaas <bjorn.helgaas@hp.com>

The current serial console code only works for ports that are either
defined in SERIAL_PORT_DFNS (and set up by serial8250_isa_init_ports()) or
registered by early_serial_setup().

On ia64, SERIAL_PORT_DFNS is empty because we discover everything via ACPI
and PCI.  And we only use early_serial_setup() for one port described by
the HCDP firmware table.

This patch against 2.6.3-rc2 makes it work for any valid port.  If we don't
know about the port early, we just return -ENODEV from the setup()
function, which leaves the serial console disabled.  After the driver has
found all the ports, we try to register the serial console again if it
hasn't been enabled already.

I think the "port->type == PORT_UNKNOWN" test is cleaner than the
"port->ops" test -- it more clearly gets to the point of "do we know about
this port".