isci: Ensure ATA passthrough commands with RETURN_RESPONSE bit set
translate their response.

Sponsored by:	Intel
Discussed with:	scottl
MFC after:	3 days
Base the max number of SG elements on MAXPHYS.

Sponsored by:	Intel
Discussed with:	scottl, emax
MFC after:	3 days
nvme: Remove the software progress marker SET_FEATURE command during
controller initialization.

The spec says OS drivers should send this command after controller
initialization completes successfully, but other NVMe OS drivers are
not sending this command.  This change will therefore reduce differences
between the FreeBSD and other OS drivers.

Sponsored by:	Intel
MFC after:	3 days
nvme:  NVMe specification dictates 4-byte alignment for PRPs (not 8).

Sponsored by:	Intel
MFC after:	3 days