sfc: add notion of match on enc keys to MAE machinery

Extend the MAE caps check to validate that the hardware supports these
 outer-header matches where used by the driver.
Extend efx_mae_populate_match_criteria() to fill in the outer rule ID
 and VNI match fields.
Nothing yet populates these match fields, nor creates outer rules.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>