arm64: dts: qcom: pmi8994: Define MPP block

The pmi8994 has 4 multi-purpose-pins, add these to the definition.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Dylan Van Assche <me@dylanvanassche.be>
Link: https://lore.kernel.org/r/20220505022706.1692554-4-bjorn.andersson@linaro.org