net/mlx5: Introduce MACsec Connect-X offload hardware bits and structures

Add MACsec offload related IFC structs, layouts and enumerations.

Signed-off-by: Lior Nahmanson <liorna@nvidia.com>
Reviewed-by: Raed Salem <raeds@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>