Do some source && comment cleanup.

Clean out the abortive start to homegrown, per-mpt,
Domain Validation. This should really be done at a
higher level.

Use the PIM_SEQSCAN flag for U320- this seems to correct
cases of being unable to consistently negotiate U320 in
the cases where I'd seen this before.

Between this and other recent checkins, this driver is
pretty close to being ready for MFC.

Reviewed by: scottl, ken, scsi@
MFC after: 1 week