regulator: richtek,rt4801: parse GPIOs per regulator

Having one enable-gpios property for all regulators is discouraged and
instead, similarly to regulator core ena_gpiod feature, each GPIO should
be present in each regulator node.  Add support for parsing such GPIOs,
keeping backwards compatibility.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Tested-by: ChiYuan Huang <cy_huang@richtek.com>
Link: https://lore.kernel.org/r/20220425072455.27356-3-krzysztof.kozlowski@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>