net/mlx5: Unify vport manager capability check

Expose MLX5_VPORT_MANAGER macro to check for strict vport manager
E-switch and MPFS (Multi Physical Function Switch) abilities.

VPORT manager must be a PF with an ethernet link and with FW advertised
vport group manager capability

Replace older checks with the new macro and use it where needed in
eswitch.c and mlx5e netdev eswitch related flows.

The same macro will be reused in MPFS separation downstream patch.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>