This time, Lenovo decided to go with different pieces in its latest
series of Thinkpads.

For those we have been able to test:
- the T480 is using Synaptics with an IBM trackpoint
   -> it behaves properly with or without intertouch, there is no point
      not using RMI4
- the X1 Carbon 6th gen is using Synaptics with an IBM trackpoint
   -> the touchpad doesn't behave properly under PS/2 so we have to
      switch it to RMI4 if we do not want to have disappointed users
- the X280 is using Synaptics with an ALPS trackpoint
   -> the recent fixes in the trackpoint handling fixed it so upstream
      now works fine with or without RMI4, and there is no point not
      using RMI4
- the T480s is using an Elan touchpad, so that's a different story

Cc: <stable@vger.kernel.org> # v4.14.x, v4.15.x, v4.16.x
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: KT Liao <kt.liao@emc.com.tw>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>