* Synopsys DesignWare PCIe root complex in ECAM shift mode

In some cases, firmware may already have configured the Synopsys DesignWare
PCIe controller in RC mode with static ATU window mappings that cover all
config, MMIO and I/O spaces in a [mostly] ECAM compatible fashion.
In this case, there is no need for the OS to perform any low level setup
of clocks, PHYs or device registers, nor is there any reason for the driver
to reconfigure ATU windows for config and/or IO space accesses at runtime.

In cases where the IP was synthesized with a minimum ATU window size of
64 KB, it cannot be supported by the generic ECAM driver, because it
requires special config space accessors that filter accesses to device #1
and beyond on the first bus.

Required properties:
- compatible: "marvell,armada8k-pcie-ecam" or
              "socionext,synquacer-pcie-ecam" or
              "snps,dw-pcie-ecam" (must be preceded by a more specific match)

Please refer to the binding document of "pci-host-ecam-generic" in the
file host-generic-pci.txt for a description of the remaining required
and optional properties.

Example:

    pcie1: pcie@7f000000 {
        compatible = "socionext,synquacer-pcie-ecam", "snps,dw-pcie-ecam";
        device_type = "pci";
        reg = <0x0 0x7f000000 0x0 0xf00000>;
        bus-range = <0x0 0xe>;
        #address-cells = <3>;
        #size-cells = <2>;
        ranges = <0x1000000 0x00 0x00010000 0x00 0x7ff00000 0x0 0x00010000>,
                 <0x2000000 0x00 0x70000000 0x00 0x70000000 0x0 0x0f000000>,
                 <0x3000000 0x3f 0x00000000 0x3f 0x00000000 0x1 0x00000000>;

        #interrupt-cells = <0x1>;
        interrupt-map-mask = <0x0 0x0 0x0 0x0>;
        interrupt-map = <0x0 0x0 0x0 0x0 &gic 0x0 0x0 0x0 182 0x4>;
        msi-map = <0x0 &its 0x0 0x10000>;
        dma-coherent;
    };