buildworld, installworld and multiuser on Sibyte

[Neelkanth Natu]

Hi,

After a long time trying to get this to work I was finally able to do a
buildworld, installworld and boot multiuser on the Sibyte reference
platform.

I was sidetracked by two issues:

- I had one bad dimm that was causing cache error exceptions

- I was booting with more memory that can be mapped by KSEG0 - it seems
  that the pmap code doesn't support this

Anyways, this is a milestone for the SWARM platform and I thought I would
share it with the list.

best
Neel