net: phy: at803x: support qca8081 genphy_c45_pma_read_abilities

qca8081 PHY supports to use genphy_c45_pma_read_abilities for
getting the PHY features supported except for the autoneg ability

but autoneg ability exists in MDIO_STAT1 instead of MMD7.1, add it
manually after calling genphy_c45_pma_read_abilities.

Signed-off-by: Luo Jie <quic_luoj@quicinc.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>