U-Boot config options used in fec_mxc.c
  
  CONFIG_FEC_MXC
  	Selects fec_mxc.c to be compiled into u-boot. Can read out the
  	ethaddr from the SoC eFuses (see below).
  
  CONFIG_MII
  	Must be defined if CONFIG_FEC_MXC is defined.
  
  CONFIG_FEC_XCV_TYPE
  	Defaults to MII100 for 100 Base-tx.
  	RGMII selects 1000 Base-tx reduced pin count interface.
  	RMII selects 100 Base-tx reduced pin count interface.
  
  CONFIG_FEC_MXC_SWAP_PACKET
  	Forced on iff MX28.
  	Swaps the bytes order of all words(4 byte units) in the packet.
  	This should not be specified by a board file. It is cpu specific.
  
  CONFIG_PHYLIB
  	fec_mxc supports PHYLIB and should be used for new boards.
  
  CONFIG_FEC_MXC_NO_ANEG
  	Relevant only if PHYLIB not used. Skips auto-negotiation restart.
  
  CONFIG_FEC_MXC_PHYADDR
  	Optional, selects the exact phy address that should be connected
  	and function fecmxc_initialize will try to initialize it.
  
  CONFIG_FEC_FIXED_SPEED
  	Optional, selects a fixed speed on the MAC interface without asking some
  	phy. This is usefull if there is a direct MAC <-> MAC connection, for
  	example if the CPU is connected directly via the RGMII interface to a
  	ethernet-switch.
  
  Reading the ethaddr from the SoC eFuses:
  if CONFIG_FEC_MXC is defined and the U-Boot environment does not contain the
  ethaddr variable, then its value gets read from the corresponding eFuses in
  the SoC. See the README files of the specific SoC for details.