USB for ATSAMD11C

[mriise]

atsamd11c does have support for USB device, it has just not been implemented yet. I will likely open a PR as an attempt to implement it but I would love to work with someone / receive feedback during who knows more about it than me.

[ianrrees]

I've looked at it a little bit, the issue is that even a basic USB device firmware takes up the entire flash on SAMD11 - at least the one I looked at - didn't spend much time on it. A firmware for SAMD21 will be the same size, more-or-less as it would be for SAMD11.

I'm happy to help out with enabling USB on SAMD11 if it looks like there's a viable use case, but do have a few other things on the go at the moment (and none in Rust :/) so might be slow.