net: dpaa2: add support for manual setup of IRQ coalesing

Use the newly exported dpio driver API to manually configure the IRQ
coalescing parameters requested by the user.
The .get_coalesce() and .set_coalesce() net_device callbacks are
implemented and directly export or setup the rx-usecs on all the
channels configured.

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