psm(4): Probe Synaptics touchpad with active multiplexing mode enabled

if it is only multiplexed device. Also enable syncbit checks for them.
This fixes touchpad recognition on Panasonic Toughbook CF-MX4 laptop.

Reported by: Tomasz "CeDeROM" CEDRO <tomek_AT_cedro_DOT_info>
MFC after: 1 month
PR: 253279
Differential revision: https://reviews.freebsd.org/D28502