dpaa2-mac: add PCS support through the Lynx module

Include PCS support in the dpaa2-eth driver by integrating it with the
new Lynx PCS module. There is not much to talk about in terms of changes
needed in the dpaa2-eth driver since the only steps necessary are to
find the MDIO device representing the PCS, register it to the Lynx PCS
module and then let phylink know if its existence also.
After this, the PCS callbacks will be treated directly by Lynx, without
interraction from dpaa2-eth's part.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>