present and initialize a few things. No color support, yet.
- Properly disable interrupts for DAFB.
- Rearrange for better nubus display card interrupt support. Only register
an interrupt if we know how to clear it.
- Complain if we don't know about a given display card and can not install
an interrupt handler.
- Change MYSTERY stuff to cb264--still need to get the DrSW so we can
actually call the routine to clear an interrupt from this card.