net: dsa: b53/bcm_sf2: implement .support_eee() method

Implement the .support_eee() method to indicate that EEE is not
supported by two switch variants, rather than making these checks in
the .set_mac_eee() and .get_mac_eee() methods.

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-006cZU-Nc@rmk-PC.armlinux.org.uk


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