Keep track of negotiated transfer parameters for each initiator<->target

Keep track of negotiated transfer parameters for each initiator<->target
connection.

Clean up support for devices featuring the multiple target SCSI ID feature.
On aic7890/91/96/97 chips, we can now assume the target role on multiple
target ids simultaneously.  Although these chips also have sufficient
instruction space to hold to support the initiator and target role at the
same time, the initiator role is currently disabled as it will conflict
(chip design restriction) with the multi-tid feature.  I'll probably add
a nob to enable the initiator (there-by disabling multi-tid) some time
in the future.

Return queue full or busy, depending on the tagged nature of the incoming
request, if our command input queue fills up in host memeory.

Deal with accept target I/O resource shortages.

If we get an underrun on a transaction that wasn't supposed to transmit
any data, don't attempt to print out the S/G list.  The code would
run until hitting a non-present page. (oops)