arm64: dts: qcom: pmi8994: add missing MPP compatible fallback

Bindings require usage of generic MPP fallback in compatible:

  qcom/apq8094-sony-xperia-kitakami-karin_windy.dtb: pmic@2: mpps@a000:compatible: ['qcom,pmi8994-mpp'] is too short

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220908081050.29751-1-krzysztof.kozlowski@linaro.org