[SCSI] mpt2sas: Added raid transport support

Adding support for raid transport layer.  This will provide sysfs attributes
containing raid level, state, and resync rate.

MPT2SAS module will select RAID_ATTRS.

Signed-off-by: Kashyap Desai <kashyap.desai@lsi.com>
Reviewed-by: Eric Moore <eric.moore@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>