scsi: Add scsi_vpd_tpg_id()

Implement scsi_vpd_tpg_id() to extract the target
port group id and the relative port id from
SCSI VPD page 0x83.

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