dt-bindings: arm: qcom: document sda660 SoC and ifc6560 board

Add binding documentation for the Inforce IFC6560 board which uses
Snapdragon SDA660.

Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220521202708.1509308-11-dmitry.baryshkov@linaro.org