psm(4): Disable AUX multiplexer probing on all Lenovo laptops.

Rudimentary AUX multiplexing support was added to kernel to make possible
touchpad initialization on some HP EliteBook laptops with trackpoint.

Disable multiplexer probing on all Lenovo laptops now as they use touchpad
pass-through port rather than AUX multiplexer to connect trackpoint and
at least two model (X120e and X121e) is known for getting PS/2 AUX port
dysfunctional after switching back to hidden multiplexing mode.

AUX MUX probing can be reenabled with setting of hw.psm.mux_disabled loader
tunable to 0.

PR: 249987
Reported by: jwb
MFC after: 2 weeks