dt-bindings: arm: qcom: Add missing schema for MSM8974

The SoC/board bindings for MSM8974 are undocumented. Add the missing
bindings to the schema.

Cc: Andy Gross <agross@kernel.org>
Cc: David Brown <david.brown@linaro.org>
Cc: linux-arm-msm@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/qcom.yaml

@@ -101,6 +101,15 @@ properties:
               - qcom,msm8960-cdp
           - const: qcom,msm8960
 
+      - items:
+          - enum:
+              - fairphone,fp2
+              - lge,hammerhead
+              - sony,xperia-amami
+              - sony,xperia-castor
+              - sony,xperia-honami
+          - const: qcom,msm8974
+
       - items:
           - const: qcom,msm8916-mtp/1
           - const: qcom,msm8916-mtp