PSX16550 serial now uses MI com(4)

Hi,

I've committed changes to switch PSX16550 fast serial board driver
to using MI com(4) driver.
http://mail-index.NetBSD.org/source-changes/2012/04/29/msg034022.html

You have to update your kernel config files like:

-xcom0	at mainbus0			# NS16550 fast serial
-xcom1	at mainbus0
+com0	at intio0 addr 0xefff00 intr 240	# PSX16550, port1
+com1	at intio0 addr 0xefff10 intr 241	# PSX16550, port2

as seen in x68k/conf/GENERIC rev 1.161, even if you don't use PSX16550.

Note TL16C550CN on PSX16550 seems to have some timing critical issue
around THRE (TX hold register empty) interrupt and I (and isaki@)
were annoyed by "no intterupt after TX" problem during debugging,
but old MD xcom driver had the similar problem and at least login
from ttyC0 works with committed sources on my X68030.

Have fun,
---
Izumi Tsutsui