powerpc/p2041rdb: Add ethernet support on P2041RDB board

Add support for RGMII, SGMII and XAUI Ethernet on P2041RDB board.

The five dTSEC can be routed to two on-board RGMII phy, three on-board
SGMII phy or four SGMII phy on SGMII riser card according to different
serdes protocol configuration and board lane configuration. Also updated
the device tree to direct the Fmac MAC to the correct PHY.

Removed CONFIG_SYS_FMAN_FW as its not used anywhere.

Signed-off-by: Mingkai Hu <Mingkai.hu@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>