dt-bindings: PCI: qcom: Add MHI registers for IPQ9574

dt-bindings: PCI: qcom: Add MHI registers for IPQ9574

The MHI registers are present in IPQ5332, IPQ6018, IPQ8074 and IPQ9574
SoCs. Hence, add the MHI registers to the binding to allow these registers
to be defined in devicetree.

Signed-off-by: Varadarajan Narayanan <quic_varada@quicinc.com>
[mani: commit message rewording]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20250317100029.881286-2-quic_varada@quicinc.com