scsi: core: add SPDX tags to scsi midlayer files missing licensing information

Add the default kernel GPLv2 annotation to SCSI midlayer files missing any
licensing information.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>