r8169: fix PHY driver check on platforms w/o module softdeps

On Android/x86 the module loading infrastructure can't deal with
softdeps. Therefore the check for presence of the Realtek PHY driver
module fails. mdiobus_register() will try to load the PHY driver
module, therefore move the check to after this call and explicitly
check that a dedicated PHY driver is bound to the PHY device.

Fixes: f3259377 ("r8169: check that Realtek PHY driver module is loaded")
Reported-by: Chih-Wei Huang <cwhuang@android-x86.org>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>