net/mlx5: Add support for multiple RoCE enable

Previously, only mlx5_ib enabled RoCE on the port, but FPGA needs it as
well.
Add support for counting number of enables, so that FPGA and IB can work
in parallel and independently.
Program the HW to enable RoCE on the first enable call, and program to
disable RoCE on the last disable call.

Signed-off-by: Ilan Tayari <ilant@mellanox.com>
Reviewed-by: Boris Pismenny <borisp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>