powerpc/85xx: Add FMan ethernet support to P4080DS

Add support for RGMII, SGMII, and XAUI (10Gb) Ethernet on P4080DS.

The board supports add-on cards for SGMII and XAUI functionality.  Which
slots on the board these cards are in is a function of the SERDES option
selected and muxes on the board.

Additionally because of the high-configurablity which MDIO bus one is
connected to is "selected" via an FPGA register.  We create dummy MDIO
bus for the phy layer and hide the mux manipulation in this dummy layer.

Add fman fdt helper function in board common code it'll be used by several
freescale boards that do various muxing of the MDIO signals based on which
controller/interface one is trying to talk to.

Removed CONFIG_SYS_FMAN_FW as its not used anywhere.

Signed-off-by: Mingkai Hu <Mingkai.hu@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>