net: mvpp2: RSS indirection table support

This patch adds the RSS indirection table support, allowing to use the
ethtool -x and -X options to dump and set this table.

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
[Maxime: Small warning fixes, use one table per port]
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>