dt-bindings: PCI: qcom: Add IPQ8074 Gen3 port

IPQ8074 has one Gen2 and one Gen3 PCIe port, with Gen2 already supported.
Document Gen3 port which uses the same controller as IPQ6018.

Link: https://lore.kernel.org/r/20230113164449.906002-6-robimarko@gmail.com


Signed-off-by: Robert Marko <robimarko@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>