touchpad: pretend the jumpy semi-mt touchpad is a single-touch touchpad

touchpad: pretend the jumpy semi-mt touchpad is a single-touch touchpad

The first finger is accurate, it's just the second finger that is imprecise,
so we can't handle it as a true touch. Instead, revert the device back to
being a single-touch touchpad and use the fake touch bits for second finger
handling.

Two-finger scrolling thus becomes usable though we will lose out on
other features like thumb detection. Useful scrolling trumps that though.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>