Set ftgmac100 mac address on boot

[madscientist159]

The Firestone BMC (re)boots every time with a different, random MAC address on the BMC Ethernet port, even with the "ethaddr" u-boot environment variable set and saved to Flash.

Running "dhcp" before "boot" allows the saved MAC address to be used; this action initializes the hardware and sets the MAC address in the hardware registers.

[shenki]

See openbmc/openbmc#578 for discussion.

I think this is a side effect of some changes made a while back to not initialise the network hardware unless a network command was performed.

I think we want to program the ftgmac100 register regardless, so the kernel can pick up the correct MAC address for its interfaces.

When we move to u-boot passing the device tree to the kernel, we can also have the mac address added to the device tree.