mlxsw: acl: Introduce mcrouter ACL action

The Spectrum multicast forwarding is done using an ACL action. Add the
mcrouter ACL action that will be used to offload the multicast router
logic.

Signed-off-by: Yotam Gigi <yotamg@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>