scsi: 3w-9xxx: Reduce scope of structure packing

Currently, all command packet structs used by this driver are packed.
However, only one (TW_SG_Entry) actually needs to be packed, because it
uses 64-bit addresses at 32-bit alignment. To improve the quality of
generated code, stop packing all of the other command packet structs.  This
requires adjusting the type of one misaligned "reserved" member.

After this change, pahole reports that only one type had its layout change:
the tw_compat_info member of TW_Device_Extension is now naturally aligned.

Link: https://lore.kernel.org/r/20210427235915.39211-3-samuel@sholland.org


Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>