net/mlx5: Move devlink registration before mlx5_load

In order to allow reference to devlink parameters during driver load,
move the devlink registration before mlx5_load. Subsequent patch will
use it to control the number of completion vectors required based on
whether eth is enabled or not.

Signed-off-by: Eli Cohen <elic@nvidia.com>
Reviewed-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>