Functional AW on Win10 UAC2 driver

[Børge Strand-Bergesen]

Hi guys, 

long story short: latest push to github in audio-widget-experimental branch is an Audio Widget which is supported by the Win10 Creators Update UAC2 driver. I have just tested and measured all 6 classical sample rates.

This was one h*** of a debug! I almost sacrificed a goat here. I got good help on Upwork and from a friend of mine. 

The code in the repo now is ugly as hell. I'll spend the next few days cleaning it up and testing it on multiple platforms. Feel free to build and try, it probably won't break your hardware. But read the messy state of the code and it will break your hearts :-) 

What did I do?

- Temporarily removed the interface used by Widget Control. Will put it back in in the end

- Cut unused HID RX EP

- Added descriptive names "Analog_L" and "Analog_R" for _AS_ interfaces and terminal units

- Redefined capabilities of input terminal and clock source

- Learned that the Win10 driver has a very hard time with sample rate triplets with range

- Redefined the sample rates as 6 single-frequency triplets

- Recycled long-descriptor-reporting code as send_descriptor() to fit 6 triplets in 64-byte EP0

- Resynced DMA+I2S setup to avoid L/R channel swaps (not really part of Win10 driver)

I hope you will assist me in beta testing the firmware next week. It should work on all AB boards from me and those inspired by their schematics. 

Børge