Add PIM_SEQSCAN for HBA misc flags and code that understands

Add PIM_SEQSCAN for HBA misc flags and code that understands
what to do with it.

This forces us to scan targets sequentially, not in parallel.
The reason we might want to do this is that SPI negotiation
might not work right at the SIM level if we try to do it
in parallel.

If PIM_SEQSCAN is not set (default), the original behaviour for
probing is unchanged.

LUN probing is still done in parallel for each target in either
case.

Obtained-from: FreeBSD