Rewrite the FX2 firmware to be understandable

[mithro]

From @mithro on January 10, 2016 6:30

The FX2 firmware is currently really hard to understand. We should rewrite it to make it easier to understand an extend.

This has been started by @mithro at https://github.com/mithro/HDMI2USB-misoc-firmware/tree/fx2-refactor

The big changes so far are;

• Using the Linux headers for ch9 and uvc constants.
• Using the Linux headers to build the descriptors.
  • See https://github.com/mithro/fx2lib-linux-headers
• Actually using comments and links to the spec documentation.
• Using C99 rather then C89.
• Start for actually support the UVC control commands.
  • Need to figure out a way to communicate the information to the FPGA.

Copied from original issue: timvideos/HDMI2USB-litex-firmware#149

[mithro]

This will fix https://github.com/timvideos/HDMI2USB-misoc-firmware/issues/148 - UVC non compliance - GET_DEF(PROBE) not supported