Input: alps - don't handle ALPS cs19 trackpoint-only device

On a latest Lenovo laptop, the trackpoint and 3 buttons below it
don't work at all, when we move the trackpoint or press those 3
buttons, the kernel will print out:
"Rejected trackstick packet from non DualPoint device"

This device is identified as an alps touchpad but the packet has
trackpoint format, so the alps.c drops the packet and prints out
the message above.

According to XiaoXiao's explanation, this device is named cs19 and
is trackpoint-only device, its firmware is only for trackpoint, it
is independent of touchpad and is a device completely different from
DualPoint ones.

To drive this device with mininal changes to the existing driver, we
just let the alps driver not handle this device, then the trackpoint.c
will be the driver of this device if the trackpoint driver is enabled.
(if not, this device will fallback to a bare PS/2 device)

With the trackpoint.c, this trackpoint and 3 buttons all work well,
they have all features that the trackpoint should have, like
scrolling-screen, drag-and-drop and frame-selection.

Signed-off-by: XiaoXiao Liu <sliuuxiaonxiao@gmail.com>
Signed-off-by: Hui Wang <hui.wang@canonical.com>
Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>