Platform: x86: chromeos_laptop - Add Pixel Trackpad

Instantiate the atmel mxt224s trackpad on this system.
The trackpad may appear at two possible addresses:
0x4b in operational mode.
0x25 in bootloader mode.

Signed-off-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>