VXT2000 support

Since I received a VXT2000+ last thursday, I have added support for the
VXT2000 and VXT2000+ terminals in OpenBSD-CURRENT. These machines boot
multiuser over the network (since they don't have storage devices). The
next vax snapshot will contain this code.

On the color models (which I guess are called VXT2000+), all the
on-board devices are supported, except for the parallel port. This
means you can either use it with a serial console, or a regular keyboard
and video console. You can even run X11 - it's slow as there is
currently no support for the frame buffer acceleration features, but it
nevertheless works out of the box.

On the monochrome models (which I guess are called VXT2000, without the
plus sign), all the on-board devices but the frame buffer and the
parallel port are supported.

Of course, these machines are quite slow - their horsepower is similar
to the VAXstation 4000/VLC (they have almost the same CPU), but being
diskless they will be even slower than a VLC. This means crypto stuff
takes its time... but nevertheless completes.

Here is a dmesg from my machine:

OpenBSD 4.0-beta (GENERIC) #432: Tue Aug 29 22:28:38 GMT 2006
    [email protected]:/usr/src/sys/arch/vax/compile/GENERIC
VXT2000 [14000006 08050002]
cpu: KA48
total memory = 18735104
avail memory = 13807616
using 254 buffers containing 1040384 bytes of memory
mainbus0 (root)
vxtbus0 at mainbus0
ze0 at vxtbus0: address 08:00:2b:2b:6c:6d
qsc0 at vxtbus0
lkkbd0 at qsc0 line 2
wskbd0 at lkkbd0: console keyboard
lkms0 at qsc0 line 3
wsmouse0 at lkms0
lcspx0 at vxtbus0
lcspx0: 1280x1024x8 frame buffer
wsdisplay0 at lcspx0: console (std, vt100 emulation), using wskbd0
led0 at mainbus0
booted from device: ze0
lkkbd0: LK-401 keyboard
nfs_boot: using interface ze0, with revarp & bootparams
nfs_boot: client_addr=10.0.1.190
nfs_boot: server_addr=10.0.1.101 hostname=lidenne
root on 10.0.1.101:/netboot/lidenne/root
WARNING: no TOY clock -- CHECK AND RESET THE DATE!
swap on 10.0.1.101:/netboot/lidenne/swap

Miod