RDMA/core: Validate integrity handover device cap

Protect the case that a ULP tries to allocate a QP with signature
enabled flag while the LLD doesn't support this feature.
While we're here, also move integrity_en attribute from mlx5_qp to
ib_qp as a preparation for adding new integrity API to the rw-API
(that is part of ib_core module).

Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Israel Rukshin <israelr@mellanox.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>