usb: Check against explicit use of 1209/7D00 VID/PID pair
usb: Check against explicit use of 1209/7D00 VID/PID pair

That pair is reserved for cases when it can be set implicitly by the
build system.

The check could just as well be done in sys/include/usb.h, but this
gives prettier output.

OTAkeys/RIOT,kaspar030/RIOT,authmillenon/RIOT,OlegHahm/RIOT,ant9000/RIOT,jasonatran/RIOT,kaspar030/RIOT,authmillenon/RIOT,jasonatran/RIOT,miri64/RIOT,kYc0o/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,miri64/RIOT,kaspar030/RIOT,OlegHahm/RIOT,miri64/RIOT,ant9000/RIOT,OTAkeys/RIOT,ant9000/RIOT,authmillenon/RIOT,ant9000/RIOT,kYc0o/RIOT,jasonatran/RIOT,OTAkeys/RIOT,miri64/RIOT,OTAkeys/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,ant9000/RIOT,authmillenon/RIOT,kaspar030/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,miri64/RIOT,jasonatran/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,jasonatran/RIOT