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.orgSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>