net: dsa: require .support_eee() method to be implemented

Now that we have updated all drivers, switch DSA to require an
implementation of the .support_eee() method for EEE to be usable,
rather than defaulting to being permissive when not implemented.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://patch.msgid.link/E1tL14e-006cZy-AT@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>