Hi,

I've committed this patch which adds the capability to implement 
passthrough for each upstream interface of a bus arbitrator 
independently. Previously, the passthrough could only be enabled for the 
arbitrator as a whole. This is useful when one or more components 
upstream of the arbitrator need access to components downstream of the 
arbitrator without arbitration while still requiring arbitration for 
other upstream components.

The implementation is achieved by passing the index of the upstream 
accessor to the virtual check_passthough method. The default 
implementation supports no explicit upstream passthough and checks only 
for passthrough required by the system state.

This patch also adds a virtual method which defines the latency of 
accessing the bus arbitrator itself. The default latency is 0 cycles.

Dave