regulator: dt-bindings: samsung,s2mps14: add lost samsung,ext-control-gpios

The samsung,ext-control-gpios property was lost during conversion to DT
schema:

  exynos3250-artik5-eval.dtb: pmic@66: regulators:LDO11: Unevaluated properties are not allowed ('samsung,ext-control-gpios' was unexpected)

Fixes: ea98b9eb ("regulator: dt-bindings: samsung,s2m: convert to dtschema")
Cc: <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230120131447.289702-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Mark Brown <broonie@kernel.org>