net: phy: realtek: support NBase-T MMD EEE registers on RTL8125

Emulate the 802.3bz MMD EEE registers for 2.5Gbps EEE on RTL8125.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>