net: phy: realtek: improve mmd register access for internal PHY's

r8169 provides the MDIO bus for the internal PHY's. It has been extended
with c45 access functions for addressing MDIO_MMD_VEND2 registers.
So we can switch from paged access to directly addressing the
MDIO_MMD_VEND2 registers.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/a5f2333c-dda9-48ad-9801-77049766e632@gmail.com


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