lan78xx: enable auto speed configuration for LAN7850 if no EEPROM is detected

Same as LAN7800, LAN7850 can be used without EEPROM. If EEPROM is not
present or not flashed, LAN7850 will fail to sync the speed detected by the PHY
with the MAC. In case link speed is 100Mbit, it will accidentally work,
otherwise no data can be transferred.

Better way would be to implement link_up callback, or set auto speed
configuration unconditionally. But this changes would be more intrusive.
So, for now, set it only if no EEPROM is found.

Fixes: e69647a1

 ("lan78xx: Set ASD in MAC_CR when EEE is enabled.")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20240222123839.2816561-1-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>