Added cxgb4i iSCSI driver.

This patch implements the cxgb4i iscsi connection acceleration for the
open-iscsi initiator.

The cxgb4i driver offers the iscsi PDU based offload:
- digest insertion and verification
- payload direct-placement into host memory buffer.
Signed-off-by: Karen Xie <kxie@chelsio.com>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>