platform/chrome: cros_kbd_led_backlight: support OF match

For letting device tree based machines to use the driver, support OF match.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Link: https://lore.kernel.org/r/20220523090822.3035189-5-tzungbi@kernel.org