mlx5/core: Support max_io_eqs for a function

Implement get and set for the maximum IO event queues for SF and VF.
This enables administrator on the hypervisor to control the maximum
IO event queues which are typically used to derive the maximum and
default number of net device channels or rdma device completion vectors.

Reviewed-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>