[U-Boot] implement usb gadget ethernet in uboot

[Remy Bohmer]

Hello Mike,

>> Please take a look at the CDC branch in u-boot-usb.
>> Patches to add more boards/devices or other improvements are welcome.
> feel free to yell at me for not reading some README, but any plans on merging
> back into mainline ?

Of course, but there are still some cleanups pending for which I did
not had the time lately.
It was not mainline-ready at the time I started to put it there, and I
only made it public to help others not reinventing the wheel.
Maybe I get into it next week.

Kind Regards,

Remy