net: phy: Add phy_support_eee() indicating MAC support EEE

In order for EEE to operate, both the MAC and the PHY need to support
it, similar to how pause works. With some exception - a number of PHYs
have SmartEEE or AutoGrEEEn support in order to provide some EEE-like
power savings with non-EEE capable MACs.

Copy the pause concept and add the call phy_support_eee() which the MAC
makes after connecting the PHY to indicate it supports EEE. phylib will
then advertise EEE when auto-neg is performed.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20240302195306.3207716-6-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>