This
* renames DEFAULT_xID to USB_xID_TESTING as it is not really a default
(if anyting, the 7D00 is, and it's not that)
* moves the check into Makefile
* generalizes the check to all test PID/VID pairs
* in doing so, fixes the "or" (which would have ruled out warning-free
use of an allocated pid.codes number), and compares to the actual
testing PID rather than the RIOT-peripheral PID
* removes all occurrences of duplicated checks in examples or tests,
leaving definitions only where they are needed
* moves the Kconfig defaults of the usbus_minimal example into the main
Kconfig, as these are good defaults for all cases when USB is enabled
manually
Closes: https://github.com/RIOT-OS/RIOT/issues/12273
