Add support for Pi Pico via usb-raw

[andrewdavidmackenzie]

Uses different hardware so will need to use different embassy modules.
add a feature for "pico"
Change the hardware description returned accordingly.

[andrewdavidmackenzie]

Now is discovered by piggui over usb.
Will require #625
to be able to do anything useful, as without wifi, there is nothing to configure.