dpaa2-eth: add support for TBF offload

React to TC_SETUP_QDISC_TBF and configure the egress shaper as
appropriate with the maximum rate and burst size requested by the user.
TBF can only be offloaded on DPAA2 when it's the root qdisc, ie it's a
per port shaper.

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