RDMA/mlx5: Move rep into port struct

In preparation of moving into a model of single IB device multiple ports
move rep to be part of the port structure. We mark a representor device by
setting is_rep, no functional change with this patch.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>