Jerome provided the information that also the GXL internal PHY doesn't
support MMD register access and EEE. MMD reads return 0xffff, what
results in e.g. completely wrong ethtool --show-eee output.
Therefore use the MMD dummy stubs.

Fixes: d853d145 ("net: phy: add an option to disable EEE advertisement")
Suggested-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/84432fe4-0be4-bc82-4e5c-557206b40f56@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>