psm(4): detect Lenovo top-button clickpads

libinput has special handling for Lenovo ThinkPad *40 series, where it
treats clicks on the top button area as if they came from the TrackPoint:
https://wayland.freedesktop.org/libinput/doc/latest/t440-support.html

Detect these devices and set the corresponding evdev property.

Submitted by: Greg V <greg@unrelenting.technology>
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D18676