dpaa2-eth: Refactor xps code

Move the code configuring xps on the netdev TX queues to a
separate function. A subsequent patch will need to call
this in another context as well.

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