RDMA/mlx4: Separate creation of RWQ and QP

The mlx4 WQ is implemented with HW QP without special HW object.  Current
implementation which tried to reuse the code did it with common QP
creation flows. Such decision caused to the absence of mlx4_ib_wq struct,
which is needed to ensure proper allocation of ib_wq inside of IB/core.

Separate create_qp_common() to pure QP flow and to create_rq() for RWQ.

Link: https://lore.kernel.org/r/20190704130936.8705-2-leon@kernel.orgSigned-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>