[SCSI] mpt2sas: Added multisegment mode support for Linux BSG Driver

Added support for Block IO requests with multiple segments (vectors) in
the SMP handler of the SAS Transport Class. This is required by the
BSG driver. Multisegment support added for both, Request and Response.

Signed-off-by: Nagalakshmi Nandigama <nagalakshmi.nandigama@lsi.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>