platform/chrome: chromeos_laptop - Add Elan touchpad for Wolf

The upcoming Elan Wolf (Dell Chromebook 11) devices need to know to look
for Elan touchpads on the i2c bus so that they will be functional.

Based on the chromeos-kernel commit :
https://chromium-review.googlesource.com/198283



Signed-off-by: Charlie Mooney <charliemooney@chromium.org>
Signed-off-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Olof Johansson <olof@lixom.net>