net/mlx5: Covert devlink params registration to use devlink_params_register/unregister()

Since mlx5 is the only user of devlink API to register/unregister a
single param, convert it to use array registration function allowing to
simplify the devlink API by removing the single param registration
functions.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>