dt-bindings: soc: qcom: spm: Add MSM8939 CPU compatible

Document the "qcom,msm8939-saw2-v3.0-cpu" compatible for the CPU
Subsystem Power Manager (SPM) on the MSM8939 SoC.

Signed-off-by: Vincent Knecht <vincent.knecht@mailoo.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221019171004.1080911-1-vincent.knecht@mailoo.org