net: cadence: macb: add ethtool EEE support

net: cadence: macb: add ethtool EEE support

Implement get_eee and set_eee ethtool ops for GEM as simple passthroughs
to phylink_ethtool_get_eee() and phylink_ethtool_set_eee().

No MACB_CAPS_EEE guard is needed: phylink returns -EOPNOTSUPP from both
ops when mac_supports_eee is false, which is the case when
lpi_capabilities and lpi_interfaces are not populated. Those fields are
only set when MACB_CAPS_EEE is present (previous patch), so phylink
already handles the unsupported case correctly.

Reviewed-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>
Reviewed-by: Théo Lebrun <theo.lebrun@bootlin.com>
Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
Link: https://patch.msgid.link/20260304105432.631186-4-nb@tipi-net.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>