platform/chrome: Add support for the acer c720p touchscreen.

Add support for the acer c720p touchscreen.
Tested manually by using the touchscreen on the acer c720p-2664

Based on the following patch by Dave Parker <dparker@chromium.org>:
https://chromium-review.googlesource.com/#/c/167136/

Signed-off-by: Michael Mullin <masmullin@gmail.com>
Reviewed-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Olof Johansson <olof@lixom.net>