r8169: add helper rtl8125_phy_param

The integrated PHY's of RTL8125/8126 have an own mechanism to access
PHY parameters, similar to what r8168g_phy_param does on earlier PHY
versions. Add helper rtl8125_phy_param to simplify the code.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://patch.msgid.link/847b7356-12d6-441b-ade9-4b6e1539b84a@gmail.com


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