net: dsa: realtek: provide own phylink MAC operations

Convert realtek to provide its own phylink MAC operations, thus
avoiding the shim layer in DSA's port.c. We need to provide a stub for
the mandatory mac_config() method for rtl8366rb.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/E1s11qJ-00AHi0-Kk@rmk-PC.armlinux.org.uk


Signed-off-by: Paolo Abeni <pabeni@redhat.com>