RDMA/mlx4: Embed GSI QP into general mlx4_ib QP

Refactor the storage struct of mlx4 GSI QP to be embedded in mlx4_ib
QP. This allows to remove internal memory allocation of QP struct which is
hidden inside the mlx4_ib_create_qp() flow.

Link: https://lore.kernel.org/r/20200926102450.2966017-6-leon@kernel.org
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>