dt-bindings: phy: qcom,qusb2: Document IPQ9574 compatible

Document the compatible string used for the qusb2 phy in IPQ9574.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Varadarajan Narayanan <quic_varada@quicinc.com>
Link: https://lore.kernel.org/r/d55c95a6bfeef3f49fdbcde9bc97157374e81a65.1683630932.git.quic_varada@quicinc.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>