dt-bindings: arm: cpus: Document "qcom,msm8909-smp" enable-method

MSM8909 is a fairly old 32-bit SoC without PSCI support, so the
additional CPU cores need to be initialized with a custom enable-method.
Fortunately it works just like on MSM8226 and MSM8916 so just add
an additional compatible as alias to the DT schema.
Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220705143523.3390944-8-stephan.gerhold@kernkonzept.com

Documentation/devicetree/bindings/arm/cpus.yaml

@@ -221,6 +221,7 @@ properties:
           - qcom,kpss-acc-v1
           - qcom,kpss-acc-v2
           - qcom,msm8226-smp
+          - qcom,msm8909-smp
           # Only valid on ARM 32-bit, see above for ARM v8 64-bit
           - qcom,msm8916-smp
           - renesas,apmu