Use generic config_init callback also for KSZ8021 and KSZ8031.

This has been avoided this far due to commit b838b4ac ("phy/micrel:
KSZ8031RNL RMII clock reconfiguration bug"), which claims that the PHY
becomes unresponsive if the broadcast-disable flag is set before
configuring the clock mode.

Turns out that the problem seemingly worked-around by the above
mentioned commit was really due to a hardware-configuration issue, where
the PHY was in fact strapped to address 3 rather than 0.
Tested-by: Bruno Thomsen <bth@kamstrup.dk>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>