Input: synaptics - tell users to report when they should be using rmi-smbus

Users should really consider switching to rmi-smbus instead of plain PS/2.
Notify them that they should report a missing pnpID in the file.

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