net: Rework pasemi_mac driver to use of_mdio infrastructure

This patch simplifies the driver by making use of more common code.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Tested-by: Olof Johansson <olof@lixom.net>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>