input: Add a new dummy device that reads from stdin

Currently this only allows to quit the application if return is
pressed.

Signed-off-by: Guillaume Clement <gclement@baobob.org>
input: Ignore registering NULL devices.

This will allow to write register_input(queue, open_device());

Signed-off-by: Guillaume Clement <gclement@baobob.org>
desco: Stop if a key is pressed.

Also, don't way up to 5 seconds for the touchpad to come up. We need
to find a better way for this feature.

Signed-off-by: Guillaume Clement <gclement@baobob.org>