RDMA/mlx5: Reduce QP table exposure

driver.h is common header to whole mlx5 code base, but struct
mlx5_qp_table is used in mlx5_ib driver only. So move that struct
to be under sole responsibility of mlx5_ib.

Link: https://lore.kernel.org/r/bec0dc1158e795813b135d1143147977f26bf668.1685953497.git.leon@kernel.org


Signed-off-by: Leon Romanovsky <leonro@nvidia.com>