scsi: remove abuses of scsi_populate_tag

Unless we want to build a SPI tag message we should just check SCMD_TAGGED
instead of reverse engineering a tag type through the use of
scsi_populate_tag_msg.

Also rename the function to spi_populate_tag_msg, make it behave like the
other spi message helpers, and move it to the spi transport class.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Reviewed-by: Hannes Reinecke <hare@suse.de>

drivers/scsi/53c700.c

@@ -1427,7 +1427,7 @@ NCR_700_start_command(struct scsi_cmnd *SCp)
 	if((hostdata->tag_negotiated & (1<<scmd_id(SCp)))
 	   && (slot->tag != SCSI_NO_TAG && SCp->cmnd[0] != REQUEST_SENSE &&
 	       slot->flags != NCR_700_FLAG_AUTOSENSE)) {
-		count += scsi_populate_tag_msg(SCp, &hostdata->msgout[count]);
+		count += spi_populate_tag_msg(&hostdata->msgout[count], SCp);
 	}
 
 	if(hostdata->fast &&