touchpad: disable the pressure axes wherever the resolution is nonzero

touchpad: disable the pressure axes wherever the resolution is nonzero

The kernel/udev set the pressure resolution to nonzero to indicate the value
is in a known scale (units/g). We use that information to disable the
pressure axis on such devices - real pressure cannot be translated to
contact size.

For the kernel patch see:
https://www.spinics.net/lists/linux-input/msg71237.html

Fixes #569

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