phylib: two dynamic mii_bus allocation fallout fixes

1. arch/powerpc/platforms/pasemi/gpio_mdio.c also needs to be
   converted over to mdiobus_{alloc,free}().

2. drivers/net/phy/fixed.c used to embed a struct mii_bus into its
   struct fixed_mdio_bus and then use container_of() to go from the
   former to the latter.  Since mii bus structures are no longer
   embedded, we need to do something like use the mii bus private
   pointer to go from mii_bus to fixed_mdio_bus instead.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>