dt-bindings: mailbox: add compatible for the IPQ6018 SoC

Add the mailbox compatible for the IPQ6018 SoC.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kathiravan T <kathirav@codeaurora.org>
Link: https://lore.kernel.org/r/1597648720-13649-2-git-send-email-kathirav@codeaurora.orgSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Documentation/devicetree/bindings/mailbox/qcom,apcs-kpss-global.yaml

@@ -16,6 +16,7 @@ maintainers:
 properties:
   compatible:
     enum:
+      - qcom,ipq6018-apcs-apps-global
       - qcom,ipq8074-apcs-apps-global
       - qcom,msm8916-apcs-kpss-global
       - qcom,msm8994-apcs-kpss-global