dpaa_eth: enable Rx hashing control

Allow ethtool control of the Rx flow hashing. By default RSS is
enabled, this allows to turn it off by bypassing the FMan Keygen
block and sending all traffic on the default Rx frame queue.

Signed-off-by: Madalin Bucur <madalin.bucur@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>