net: dpaa2-eth: add support to query the number of queues through ethtool

The .get_channels() ethtool_ops callback is implemented and exports the
number of queues: Rx, Tx, Tx conf and Rx err.
The last two ones, Tx confirmation and Rx err, are counted as 'others'.

The .set_channels() callback is not implemented since the DPAA2
software/firmware architecture does not allow the dynamic
reconfiguration of the number of queues.

Signed-off-by: Robert-Ionut Alexa <robert-ionut.alexa@nxp.com>
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>