realtek: mdio: apply phy polling config for RTL931x

realtek: mdio: apply phy polling config for RTL931x

Apply the PHY polling configuration for RTL931x too, as previously
implemented for RTL930x. This is needed for several PHYs on that
platform to function properly.

Add another flag called 'force_res' to the phy_info struct which is for
RTL931x only. The SDK mentions this as a flag to force polling the
Realtek proprietary PHY status resolution register. Effectively, this
changes the polling to proprietary format instead of standard format,
and sets an enable bit in another private polling register field.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21515
Signed-off-by: Robert Marko <robert.marko@sartura.hr>