net: mscc: ocelot: add bonding support

Add link aggregation hardware offload support for Ocelot.

ocelot_get_link_ksettings() is not great but it does work until the driver
is reworked to switch to phylink.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>