dt-bindings: PCI: qcom: Add support for IPQ8074

Add support for the IPQ8074 PCIe controller.  IPQ8074 supports Gen 1/2, one
lane, two PCIe root complex with support for MSI and legacy interrupts, and
it conforms to PCI Express Base 2.1 specification.

Signed-off-by: Varadarajan Narayanan <varada@codeaurora.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rob Herring <robh@kernel.org>