net: phylink: add phylink managed wake-on-lan PHY speed control

net: phylink: add phylink managed wake-on-lan PHY speed control

Some drivers, e.g. stmmac, use the speed_up()/speed_down() APIs to
gain additional power saving during Wake-on-LAN where the PHY is
managing the state.

Add support to phylink for this, which can be enabled by the MAC
driver. Only change the PHY speed if the PHY is configured for
wake-up, but without any wake-up on the MAC side, as MAC side
means changing the configuration once the negotiation has
completed.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1vBrR7-0000000BLza-2PjK@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>