scsi: core: Introduce an enumeration type for the SCSI_MLQUEUE constants

scsi: core: Introduce an enumeration type for the SCSI_MLQUEUE constants

Multiple functions in the SCSI core accept an 'int reason' argument.
The 'int' type of these arguments doesn't make it clear what values are
acceptable for these arguments. Document which values are supported for
these arguments by introducing the enumeration type scsi_qc_status. 'qc'
in the type name stands for 'queuecommand' since the values passed as
the 'reason' argument are the .queuecommand() return values.

Cc: John Garry <john.g.garry@oracle.com>
Cc: Hannes Reinecke <hare@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://patch.msgid.link/20251113181730.1109331-1-bvanassche@acm.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>