dpaa2-eth: add API for Tx shaping

Add the necessary API (dpni_set_tx_shaping) for configuring the rate and
burst size of a per port shaper in DPAA2.

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