Request 7D00 and 7D01 for RIOT devices

[chrysn]

This creates an organization for RIOT-OS, and assigns

• PID 7D00 for devices that use the operating system's built-in peripherals in lieu of the hardware parts often found on development boards. (For example, most boards supported by RIOT have an on-board USB-serial adapter wired to the chip; some newer boards don't have that and rely on the main controller's USB port to be connected to the host and provide shell functionality directly).
• PID 7D01 for devices that run the RIOT-OS USB stack but run any custom software atop of that. It is similar to the test PIDs and even applies the same policy. The ID is requested primarily for the purpose of being the default PID for the example programs shipped with RIOT, but phrased as test PIDs because one expectation around the example programs is that people start tinkering with them and slowly develop their own applications from them. The RIOT build system will show a warning to users to get own PIDs when they use these codes.
• It is expected that a few more codes are requested in the future, e.g. when a USB-based DFU bootloader is implemented, or when there is a unified board testing application.

Neither of those are bound to a particular hardware platform, as RIOT supports a plethora of those. Due to the hardware abstractions provided by RIOT, the same user code running on those different boards can be regarded as the same product for the purpose of PID assignment in my opinion.

This request has been discussed on several channels beforehand, among them RIOT-OS/RIOT#12273 on the RIOT side of things.