libevdev.EV_REL.REL_<code> breaks backward compatibility

See: https://gitlab.freedesktop.org/snippets/636

Basically, and I quote @whot on IRC:

ah, shit

that's... bad

can you file a bug for that upstream please. the reason is that we generate pseudo codes for all possible codes. but they disappear once there's a defined code for it, so the REL_0B disappeared once libevdev supports REL_WHEEL_HI_RES

and that's not good, because it breaks backwards compat, and even worse it's the libevdev you run against that will break it

I guess we should store once for all the libevdev.EV_REL.REL_<code> values to prevent this in the future