evdev: Keep track of button/key press count per device

evdev: Keep track of button/key press count per device

Keep track of the number of times a given button or key is pressed on a
device. For regular mouse devices or keyboard devices, such a count will
never exceed 1, but counting button presses could help when button
presses with the same code can originate from different sources. One could
for example implement overlapping tap-drags with button presses by
having them deal with their own life-time independently, sorting out
when the user should receive button presses or not depending on the
pressed count.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>