IB/mlx5: Limit the scope of struct mlx5_bfreg_info to mlx5_ib

struct mlx5_bfreg_info is used by mlx5_ib only but is exposed to both RDMA
and netdev parts of mlx5 driver. Move that struct to mlx5_ib namespace,
clean vertical space alignment and convert lib_uar_4k from bool to
bitfield.

Link: https://lore.kernel.org/r/20200324060143.1569116-5-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>