Add support for routing initiator transactions to disabled luns to the

Add support for routing initiator transactions to disabled luns to the
black hole device.  The controller will now only accept selections if
the black hole device is present and some other target/lun is enabled
for target mode.

Handle the IGNORE WIDE RESIDUE message.  This support has not been tested.

Checkpoint work on handling ABORT, BUS DEVICE RESET, TERMINATE I/O PROCESS,
and CLEAR QUEUE messages as a target.

Fix a few problems with tagged command handling in target mode.

Wait until the sync offset counter falls to 0 before changing phase
after a data-in transfer completes as the DMA logic seems to indicate
transfer complete as soon as our last REQ is issued.

Simplify some of the target mode message handling code in the sequencer.