* Axis ARTPEC-6 PCIe interface

This PCIe host controller is based on the Synopsys DesignWare PCIe IP
and thus inherits all the common properties defined in designware-pcie.txt.

Required properties:
- compatible: "axis,artpec6-pcie", "snps,dw-pcie" for ARTPEC-6 in RC mode;
	      "axis,artpec6-pcie-ep", "snps,dw-pcie" for ARTPEC-6 in EP mode;
	      "axis,artpec7-pcie", "snps,dw-pcie" for ARTPEC-7 in RC mode;
	      "axis,artpec7-pcie-ep", "snps,dw-pcie" for ARTPEC-7 in EP mode;
- reg: base addresses and lengths of the PCIe controller (DBI),
	the PHY controller, and configuration address space.
- reg-names: Must include the following entries:
	- "dbi"
	- "phy"
	- "config"
- interrupts: A list of interrupt outputs of the controller. Must contain an
  entry for each entry in the interrupt-names property.
- interrupt-names: Must include the following entries:
	- "msi": The interrupt that is asserted when an MSI is received
- axis,syscon-pcie: A phandle pointing to the ARTPEC-6 system controller,
	used to enable and control the Synopsys IP.

Example:

	pcie@f8050000 {
		compatible = "axis,artpec6-pcie", "snps,dw-pcie";
		reg = <0xf8050000 0x2000
		       0xf8040000 0x1000
		       0xc0000000 0x2000>;
		reg-names = "dbi", "phy", "config";
		#address-cells = <3>;
		#size-cells = <2>;
		device_type = "pci";
			  /* downstream I/O */
		ranges = <0x81000000 0 0 0xc0002000 0 0x00010000
			  /* non-prefetchable memory */
			  0x82000000 0 0xc0012000 0xc0012000 0 0x1ffee000>;
		num-lanes = <2>;
		bus-range = <0x00 0xff>;
		interrupts = <GIC_SPI 148 IRQ_TYPE_LEVEL_HIGH>;
		interrupt-names = "msi";
		#interrupt-cells = <1>;
		interrupt-map-mask = <0 0 0 0x7>;
		interrupt-map = <0 0 0 1 &intc GIC_SPI 144 IRQ_TYPE_LEVEL_HIGH>,
		                <0 0 0 2 &intc GIC_SPI 145 IRQ_TYPE_LEVEL_HIGH>,
		                <0 0 0 3 &intc GIC_SPI 146 IRQ_TYPE_LEVEL_HIGH>,
		                <0 0 0 4 &intc GIC_SPI 147 IRQ_TYPE_LEVEL_HIGH>;
		axis,syscon-pcie = <&syscon>;
	};