net: dsa: add MRP support

Add support for offloading MRP in HW. Currently implement the switchdev
calls 'SWITCHDEV_OBJ_ID_MRP', 'SWITCHDEV_OBJ_ID_RING_ROLE_MRP',
to allow to create MRP instances and to set the role of these instances.

Add DSA_NOTIFIER_MRP_ADD/DEL and DSA_NOTIFIER_MRP_ADD/DEL_RING_ROLE
which calls to .port_mrp_add/del and .port_mrp_add/del_ring_role in the
DSA driver for the switch.

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