evdev: Process touch up events of single-touch devices

evdev: Process touch up events of single-touch devices

Previously only the touch up key event was used for single-touch
devices and the touch down event was generated on the first motion
event. This was breaking if the touch up and down events were sent
without a motion in-between because the evdev driver wouldn't generate
a touch down event and Weston would lose track of the number of touch
points that are down. This patch changes it to track the up and down
key events as pending events similar to how it does for multi-touch
devices.

https://bugs.freedesktop.org/show_bug.cgi?id=69759