dt-bindings: arm: qcom: Document alcatel,idol347 board

Document the alcatel,idol347 board. It was missing leading to warning:

arch/arm64/boot/dts/qcom/msm8916-alcatel-idol347.dt.yaml: /: compatible: 'oneOf' conditional failed, one must be fixed:
        Additional items are not allowed ('qcom,msm8916' was unexpected)

Signed-off-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/20210308060826.3074234-7-vkoul@kernel.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Documentation/devicetree/bindings/arm/qcom.yaml

@@ -129,6 +129,8 @@ properties:
           - const: qcom,msm8974
 
       - items:
+          - enum:
+              - alcatel,idol347
           - const: qcom,msm8916-mtp/1
           - const: qcom,msm8916-mtp
           - const: qcom,msm8916