evdev: if a device's rotation is around 180 degrees, flip the wheel

evdev: if a device's rotation is around 180 degrees, flip the wheel

For a device used upside-down, make sure the wheels correspond to the
new physical directions. There's a grace range of 20 degrees either way
since that seems like it makes sense.

For 90 degree rotation (or 270 degree) the wheel is left as-is, the
heuristics to guess what angle we want in this case is not clear enough.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>