net/mlx5: Add cap bits for multi fdb encap

If set, the firmware supports creating of flow tables with encap
enabled while VFs are configured, if we already created one
(restriction still applies on the first creation).

Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>