scsi: core: Register sysfs for SCSI workqueue

Permit scsi_wq_xxx and scsi_tmf_xxx to be bound to different CPUs to get
better isolation.

Use alloc_workqueue with WQ_SYSFS and drop __WQ_ORDERED_EXPLICIT since a
__WQ_ORDERED_EXPLICIT workqueue isn't allowed to change the CPU mask.

Link: https://lore.kernel.org/r/20200701030745.16897-2-bob.liu@oracle.com


Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Bob Liu <bob.liu@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>