dt-bindings: net: qcom,ipa: finish the qcom,smp2p example

The example using qcom,smp2p should have all necessary properties, to
avoid DT schema validation warnings.

Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220402155551.16509-2-krzysztof.kozlowski@linaro.org