#30 Enabling nubus support panics kernel

[David A. Gatwood]

The PTEG (page table entry group) fills up if you enable nubus
support and compile a kernel currently. This is due to mapping
issues caused by not being able to map and unmap hardware
pages on-the-fly. I've written routines to do this, but haven't
tested them (or even compiled them yet). It's on my to-do for this
weekend, time permitting.