dpaa2-mac: add the MC API for retrieving the version

The dpmac_get_api_version command will be used in the next patches to
determine if the current firmware is capable or not to change the
Ethernet protocol running on the MAC.

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