RDMA/core: Introduce IB_MR_TYPE_INTEGRITY and ib_alloc_mr_integrity API

This is a preparation for signature verbs API re-design. In the new
design a single MR with IB_MR_TYPE_INTEGRITY type will be used to perform
the needed mapping for data integrity operations.

Signed-off-by: Israel Rukshin <israelr@mellanox.com>
Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>