Input: appletouch - implement sensor data smoothing

Use smoothed version of sensor array data to calculate movement and add
weight to prior values when calculating average. This gives more granular
and more predictable movement.

Signed-off-by: Clinton Sprain <clintonsprain@gmail.com>
Reviewed-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>