scsi: core: Add error codes for internal SCSI midlayer use

If a driver returns:

 - DID_TARGET_FAILURE

 - DID_NEXUS_FAILURE

 - DID_ALLOC_FAILURE

 - DID_MEDIUM_ERROR

we hit a couple bugs:

1. The SCSI error handler runs because scsi_decide_disposition() has no
case statements for them and we return FAILED.

2. For SG IO the userspace app gets a success status instead of failed,
because scsi_result_to_blk_status() clears those errors.

This patch adds a new internal error code byte for use by the SCSI
midlayer.  This will be used instead of the above error codes, so we don't
have to play that clearing the host code game in
scsi_result_to_blk_status() and drivers cannot accidentally use them.

A subsequent commit will then remove the internal users of the above codes
and convert us to use the new ones.

Link: https://lore.kernel.org/r/20220812010027.8251-9-michael.christie@oracle.com


Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>