net: ethernet: ti: cpmac: use phy_ethtool_{get|set}_link_ksettings

There are two generics functions phy_ethtool_{get|set}_link_ksettings,
so we can use them instead of defining the same code in the driver.

There was a check on CAP_NET_ADMIN in cpmac_set_settings, but this
check is already done in dev_ethtool, so no need to repeat it before
calling the generic function.

Signed-off-by: Philippe Reynes <tremyfr@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>