platform/chrome: chromeos_laptop: Add Leon Touch

Add support for Leon touch devices, which is the same as
slippy/falco/peppy/wolf on the same buses using the LynxPoint-LP I2C via
the i2c-designware-pci driver.

Based on the following patch:
https://chromium-review.googlesource.com/#/c/168351/



Signed-off-by: Gene Chen <gene.chen@intel.com>
Reviewed-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Olof Johansson <olof@lixom.net>