platform/chrome: chromeos_laptop - rework i2c peripherals initialization

Instead of having separate setup() functions responsible for instantiating
i2c client for each peripheral, let's generalize the behavior and use
common code for instantiating all i2c peripherals.
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Benson Leung <bleung@chromium.org>