net: ocelot: Extend MRP

This patch extends MRP support for Ocelot. It allows to have multiple
rings and when the node has the MRC role it forwards MRP Test frames in
HW. For MRM there is no change.

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