net: ethernet: ti: am65-cpsw: Convert to PHYLINK

Convert am65-cpsw driver and am65-cpsw ethtool to use Phylink APIs
as described at Documentation/networking/sfp-phylink.rst. All calls
to Phy APIs are replaced with their equivalent Phylink APIs.

No functional change intended. Use Phylink instead of conventional
Phylib, in preparation to add support for SGMII/QSGMII modes.

Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>