bridge: switchdev: mrp: Extend MRP API for switchdev for MRP Interconnect

Implement the MRP API for interconnect switchdev. Similar with the other
br_mrp_switchdev function, these function will just eventually call the
switchdev functions: switchdev_port_obj_add/del.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>