net: dsa: felix: Add support for MRP

Implement functions 'port_mrp_add', 'port_mrp_del',
'port_mrp_add_ring_role' and 'port_mrp_del_ring_role' to call the mrp
functions from ocelot.

Also all MRP frames that arrive to CPU on queue number OCELOT_MRP_CPUQ
will be forward by the SW.

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