arm64: dts: qcom: add fallback compatible to PMIC GPIOs

The bindings require all PMIC GPIO nodes to have two compatibles -
specific followed by SPMI or SSBI fallback.  Add the fallback to fix
warnings like:

  msm8916-samsung-serranove.dtb: gpios@c000: compatible: ['qcom,pm8916-gpio'] is too short

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220507194913.261121-7-krzysztof.kozlowski@linaro.org