testevdev: Add the ability to mark a device entry as unimplemented
There are some devices for which SDL's device classification heuristic
is known not to give the ideal result. Add a way to incorporate these
into our test data, so that when the heuristic is improved we can
detect them as their intended device type, without making the test fail
before that has been implemented.
Signed-off-by: Simon McVittie <smcv@collabora.com>