[Arm-netbook] FEL protocol have been reversed

[Henrik Nordström]

Thanks to USB dumps kindly provided by others and a bit of staring at
the data the FEL USB boot protocol have now been decoded.

https://github.com/hno/Allwinner-Info/blob/master/FEL-usb/USB-protocol.txt

What remains is to

* Figuring out which memory regions are allowed to use for FEL booting.

* Modifying u-boot SPL so it can be used for FEL USB booting.

* Write a program for sending u-boot SPL via FEL USB boot to the A10
device, or write a new SPL for FEL USB booting.

* Figuring out some unknown bits. Mainly the version message sent by
BROM.

* Collect FEL data for other Allwinner/Boxchip SoCs. A13 is of primary
interest but older devices is also interesting. 

There is a simple proof of concept program at
https://github.com/hno/Allwinner-Info/blob/master/FEL-usb/fel.c which
talks to FEL to dump some memory regions. This will move into
sunxi-tools and get polished into a FEL loader.

Regards
Henrik