dpaa2-eth: Add mqprio support

Implement mqprio qdisc support by mapping traffic classes to
different hardware enqueue priorities. The maximum number of
supported traffic classes is an attribute of each DPNI object.

The traffic classes map to hardware priorities from highest (0)
to lowest (highest prio number). The skb priority information
received from the stack is used to select the hardware Tx queue
on which to enqueue the frame.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Bogdan Purcareata <bogdan.purcareata@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>