dt-bindings: soc: qcom: smd-rpm: Add IPQ9574 compatible

Document the compatible for RPM communication
over SMD for IPQ9574 SoC

Signed-off-by: Devi Priya <quic_devipriy@quicinc.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230217142030.16012-2-quic_devipriy@quicinc.com