scsi: scsi_debug: Move some tape-specific commands to separate definitions

New definitions (struct opcode_info_t) are created for READ(6),
WRITE(6), READ POSITION(10) for tape devices.

Signed-off-by: Kai Mäkisara <Kai.Makisara@kolumbus.fi>
Link: https://lore.kernel.org/r/20250310155557.2872-4-Kai.Makisara@kolumbus.fi


Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>