r8169: add PHY c45 ops for MDIO_MMD_VENDOR2 registers

r8169: add PHY c45 ops for MDIO_MMD_VENDOR2 registers

The integrated PHYs on chip versions from RTL8168g allow to address
MDIO_MMD_VEND2 registers. All c22 standard registers are mapped to
MDIO_MMD_VEND2 registers. So far the paging mechanism is used to
address PHY registers. Add support for c45 ops to address MDIO_MMD_VEND2
registers directly, w/o the paging.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/d6f97eaa-0f13-468f-89cb-75a41087bc4a@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>