dt-bindings: iio: adc: renesas,rcar-gyroadc: Miscellaneous improvements

Set limits on the number of power-domains and resets, and make them
required.

Simplify the example, and update it to match reality:
  - Convert from obsolete MSTP to CPG/MSSR bindings,
  - Examples should use #{address,size}-cells = <1>,
  - Add missing resets property,
  - Drop soc container and pinctrl properties, which are not needed in
    examples.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/7b7a13680fa24282c3407e12b5943a66a2ed9068.1666611184.git.geert+renesas@glider.be


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>