dt-bindings: pinctrl: qcom,mdm9607: do not require function on non-GPIOs

Certain pins, like SDcard related, do not have functions and such should
not be required.

Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221016170035.35014-25-krzysztof.kozlowski@linaro.org


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>