Acer C720 has touchpad and light sensor connected to a separate I2C buses.
Since the designware I2C host controller driver has two instances on this
particular machine we need a way to match the correct instance. Add support
for this and then register both C720 touchpad and light sensor.

This code is based on following patch from Benson Leung:

https://patchwork.kernel.org/patch/3074411/Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Benson Leung <bleung@chromium.org>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Olof Johansson <olof@lixom.net>