evdev: disable pressure on the Asus UX302LA touchpad

This touchpad stops sending pressure data after the first frame of the second
finger down. If the initial pressure is too light, the finger doesn't get
detected even when the pressure increases in the future.

This thing is from 2014, so let's just disable the pressure axes on it
and skip the pressure-based touch detection code. Let's hope that it doesn't
also have ghost touches on light interactions...

Fixes #145

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