When my BIOS (actually windows) disables devices, it sets the
IO-address, IRQ (and other things) to 0 or -1. This breaks when trying
to attach these devices, since UVM goes bananas trying to do things at
address zero.

There are a few ways to fix this:

1) ignore these devices in pnpbios_attachnode
2) check for this in the device match function
3) check for this in the device attach function

Which is better?

/Johan