powerpc/mpc85xx: Add MDIO bus muxing support to the board device tree(s)

Describe the PHY topology for all configurations supported by each board

Based on prior work by Andy Fleming <afleming@freescale.com>

Signed-off-by: Shruti Kanetkar <Shruti@freescale.com>
Signed-off-by: Emil Medve <Emilian.Medve@Freescale.com>
Signed-off-by: Igal Liberman <Igal.Liberman@freescale.com>
Signed-off-by: Scott Wood <oss@buserror.net>