scsi: pm80xx: Introduce read and write length for IOCTL payload structure

Removed the common length and introduce read and write length for IOCTL
payload structure.

[mkp: fixed SoB ordering]

Link: https://lore.kernel.org/r/20200316074906.9119-7-deepak.ukey@microchip.com


Acked-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: Viswas G <viswas.g@microchip.com>
Signed-off-by: Deepak Ukey <deepak.ukey@microchip.com>
Signed-off-by: Radha Ramachandran <radha@google.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>