dt-bindings: pinctrl: qcom,pmic-mpp: make compatible fallbacks specific

Instead of allowing compatibles followed by any fallback (for SPMI or
SSBI PMICs), make the list specific.

Link: https://lore.kernel.org/r/20220908080703.28643-1-krzysztof.kozlowski@linaro.org


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