dpaa2-eth: move the mqprio setup into a separate function

Move the setup done for MQPRIO into a separate function so that
with the addition of another offload we do not crowd
dpaa2_eth_setup_tc(). After this restructuring it's easier to see what
is supported in terms of Qdisc offloading.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>