dt-bindings: mfd: cros-ec: Add properties for GPIO controller

dt-bindings: mfd: cros-ec: Add properties for GPIO controller

The ChromeOS embedded controller (EC) supports setting the state of
GPIOs when the system is unlocked, and getting the state of GPIOs in all
cases. The GPIOs are on the EC itself, so the EC acts similar to a GPIO
expander. Add the #gpio-cells and gpio-controller properties to the
cros-ec binding so that other devices described in DT can get the GPIOs
on the EC.

Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240219202325.4095816-2-swboyd@chromium.org
Signed-off-by: Lee Jones <lee@kernel.org>