psm(4): Enable touchpads and trackpads by default

Enable synaptics and elantech touchpads, as well as IBM/Lenovo TrackPoints
by default, instead of having users find and toggle a loader tunable.
This makes things like two finger scroll and other modern features work out
of the box with X. By enabling these settings by default, we get a better
desktop experience in X, since xserver and evdev can make use of the more
advanced synaptics and elantech features.

Reviewed by: imp, wulf, 0mp
Approved by: imp
Sponsored by: B3 Init (zeising)
Differential Revision: https://reviews.freebsd.org/D20507