scsi: megaraid_sas: Update structures for HOST_DEVICE_LIST DCMD

Add padding to make the structure variables in MR_HOST_DEVICE_LIST_ENTRY
64-bit aligned.  Also, add reserved fields to MR_HOST_DEVICE_LIST for
future firmware usage.

Signed-off-by: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>