Cores now have an extra CoreParam, useSupervisor which was set to
the default false. Whether a core has supervisor mode is the union
of this and useVM which defaults true so not change was made by this
addition.
BusTopologies are now set with the Config system rather than a system
mixin and so all configs now include the config most similar to the
previous mixin
Testchipip was updated to be able to replace the systembus, in this
new config system, with a ring bus.
The L2 cache repo needed a similar update on how to find the buses.
It currently points to the ucb-bar fork
Treadle is bumped to its release branch
43f6083b69