Add hint to pass extra devices to libusb whitelist

[ThadHouse]

Currently, the libusb whitelist is hardcoded. However, there are times where it might be nice to force other devices to use libusb in certain cases. It'd be great if there was a hint to add extra devices to the whitelist.

[slouken]

Sure, feel free to make a PR. SDL_vidpid_list might be useful here.