Add device attribute 'sas_ncq_prio_enable' to enable SATA NCQ priority
support and provide I/O priority in SCSI command and pass priority
information to controller firmware.

This device attribute works only when device has NCQ priority support and
controller firmware can handle I/Os with NCQ priority attribute.

Link: https://lore.kernel.org/r/164375208306.440833.7392577382127815362.stgit@brunhilda.pdev.netReviewed-by: Mike McGowen <mike.mcgowen@microchip.com>
Reviewed-by: Scott Teel <scott.teel@microchip.com>
Signed-off-by: Gilbert Wu <Gilbert.Wu@microchip.com>
Signed-off-by: Don Brace <don.brace@microchip.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>