filter: replace the trackpoint accel with a velocity-based one

filter: replace the trackpoint accel with a velocity-based one

This gets rid of the trackpoint range propery that we've been parsing until
now and instead just opts for a basic curve with some deceleration for low
pressure. The speed range is taken from the touchpad and should be wide enough
for most trackpoints that fall within the expected range.

Trackpoints like the new ALPS ones need to be configured through a hwdb (this
part is currently missing).

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