phylib: Add Realtek 821x eth PHY support

this PHY present on the MPC8315E and MPC837xE RDB boards.

Signed-off-by: Johnson Leung <r58129@freescale.com>
Signed-off-by: Kevin Lam <r43770@freescale.com>
Signed-off-by: Joe D'Abbraccio <ljd015@freescale.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: David S. Miller <davem@davemloft.net>