net: phylink: add support for notifying PCS about EEE

net: phylink: add support for notifying PCS about EEE

There are hooks in the stmmac driver into XPCS to control the EEE
settings when LPI is configured at the MAC. This bypasses the layering.
To allow this to be removed from the stmmac driver, add two new
methods for PCS to inform them when the LPI/EEE enablement state
changes at the MAC.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1thRQ3-003w6u-RH@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>