net/mlx5: Introduce a helper API to check VF vport

Introduce a helper API mlx5_eswitch_is_vf_vport() to check
if a given vport_num belongs to VF or not.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Jianbo Liu <jianbol@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>