To make this work nice, big changes to the boot unit handling
was also required. From now only DEC HW unit numbering are used
in boot, to easy match boot device in kernel.
and will probably work with Massbus adapters as well. (Not tested,
but it's the same code as for 11/780). Ubareset's may cause crashes
on 8600 also like 11/780, but they are more uncommon. No support
for console RL02 yet, but it's likely to come.
