Input: synaptics - keep PS/2 around when RMI4_SMB is not enabled

Or the user might have the touchpad unbound from PS/2 but never picked
up by rmi-smbus.ko

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>