Resurrect upa(4), now used for the subordinate/slave UPA bridge and

Resurrect upa(4), now used for the subordinate/slave UPA bridge and
bus hanging off from the Fireplane/Safari bus in some USIII machines.
This is part 3/4 of allowing creator(4) to work in these machines.
The little info needed on how to configure the bridge and to work
around the incorrect values contained in the `interrupts' properties
of its children were obtained form OpenSolaris.