dt-bindings: mailbox: qcom: Add MSM8974 APCS compatible

Add compatible for the Qualcomm MSM8974 APCS block.
Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

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

@@ -30,6 +30,7 @@ properties:
           - const: syscon
       - items:
           - enum:
+              - qcom,msm8974-apcs-kpss-global
               - qcom,msm8976-apcs-kpss-global
           - const: qcom,msm8994-apcs-kpss-global
           - const: syscon