MediaTek Gen2 PCIe controller

Required properties:
- compatible: Should contain one of the following strings:
	"mediatek,mt7623-pcie"
- device_type: Must be "pci"
- reg: Base addresses and lengths of the PCIe subsys and root ports.
- reg-names: Names of the above areas to use during resource lookup.
- #address-cells: Address representation for root ports (must be 3)
- #size-cells: Size representation for root ports (must be 2)
- clocks: Must contain an entry for each entry in clock-names.
- clock-names:
  Mandatory entries:
   - sys_ckN :transaction layer and data link layer clock
  Required entries for MT7623:
   - free_ck :for reference clock of PCIe subsys
  where N starting from 0 to one less than the number of root ports.
- phys: List of PHY specifiers (used by generic PHY framework).
- phy-names : Must be "pcie-phy0", "pcie-phy1", "pcie-phyN".. based on the
  number of PHYs as specified in *phys* property.
- power-domains: A phandle and power domain specifier pair to the power domain
  which is responsible for collapsing and restoring power to the peripheral.
- bus-range: Range of bus numbers associated with this controller.
- ranges: Ranges for the PCI memory and I/O regions.

Required properties for MT7623:
- #interrupt-cells: Size representation for interrupts (must be 1)
- interrupt-map-mask and interrupt-map: Standard PCI IRQ mapping properties
  Please refer to the standard PCI bus binding document for a more detailed
  explanation.
- resets: Must contain an entry for each entry in reset-names.
- reset-names: Must be "pcie-rst0", "pcie-rst1", "pcie-rstN".. based on the
  number of root ports.

In addition, the device tree node must have sub-nodes describing each
PCIe port interface, having the following mandatory properties:

Required properties:
- device_type: Must be "pci"
- reg: Only the first four bytes are used to refer to the correct bus number
  and device number.
- #address-cells: Must be 3
- #size-cells: Must be 2
- #interrupt-cells: Must be 1
- interrupt-map-mask and interrupt-map: Standard PCI IRQ mapping properties
  Please refer to the standard PCI bus binding document for a more detailed
  explanation.
- ranges: Sub-ranges distributed from the PCIe controller node. An empty
  property is sufficient.

Examples for MT7623:

	hifsys: syscon@1a000000 {
		compatible = "mediatek,mt7623-hifsys",
			     "syscon";
		reg = <0x1a000000 0x1000>;
		#clock-cells = <1>;
		#reset-cells = <1>;
	};

	pcie: pcie@1a140000 {
		compatible = "mediatek,mt7623-pcie";
		device_type = "pci";
		reg = <0x1a140000 0x1000>, /* PCIe shared registers */
		      <0x1a142000 0x1000>, /* Port0 registers */
		      <0x1a143000 0x1000>, /* Port1 registers */
		      <0x1a144000 0x1000>; /* Port2 registers */
		reg-names = "subsys", "port0", "port1", "port2";
		#address-cells = <3>;
		#size-cells = <2>;
		#interrupt-cells = <1>;
		interrupt-map-mask = <0xf800 0 0 0>;
		interrupt-map = <0x0000 0 0 0 &sysirq GIC_SPI 193 IRQ_TYPE_LEVEL_LOW>,
				<0x0800 0 0 0 &sysirq GIC_SPI 194 IRQ_TYPE_LEVEL_LOW>,
				<0x1000 0 0 0 &sysirq GIC_SPI 195 IRQ_TYPE_LEVEL_LOW>;
		clocks = <&topckgen CLK_TOP_ETHIF_SEL>,
			 <&hifsys CLK_HIFSYS_PCIE0>,
			 <&hifsys CLK_HIFSYS_PCIE1>,
			 <&hifsys CLK_HIFSYS_PCIE2>;
		clock-names = "free_ck", "sys_ck0", "sys_ck1", "sys_ck2";
		resets = <&hifsys HIFSYS_PCIE0_RST>,
			 <&hifsys HIFSYS_PCIE1_RST>,
			 <&hifsys HIFSYS_PCIE2_RST>;
		reset-names = "pcie-rst0", "pcie-rst1", "pcie-rst2";
		phys = <&pcie0_phy PHY_TYPE_PCIE>, <&pcie1_phy PHY_TYPE_PCIE>,
		       <&pcie2_phy PHY_TYPE_PCIE>;
		phy-names = "pcie-phy0", "pcie-phy1", "pcie-phy2";
		power-domains = <&scpsys MT7623_POWER_DOMAIN_HIF>;
		bus-range = <0x00 0xff>;
		ranges = <0x81000000 0 0x1a160000 0x1a160000 0 0x00010000	/* I/O space */
			  0x83000000 0 0x60000000 0x60000000 0 0x10000000>;	/* memory space */

		pcie@0,0 {
			reg = <0x0000 0 0 0 0>;
			#address-cells = <3>;
			#size-cells = <2>;
			#interrupt-cells = <1>;
			interrupt-map-mask = <0 0 0 0>;
			interrupt-map = <0 0 0 0 &sysirq GIC_SPI 193 IRQ_TYPE_LEVEL_LOW>;
			ranges;
		};

		pcie@1,0 {
			reg = <0x0800 0 0 0 0>;
			#address-cells = <3>;
			#size-cells = <2>;
			#interrupt-cells = <1>;
			interrupt-map-mask = <0 0 0 0>;
			interrupt-map = <0 0 0 0 &sysirq GIC_SPI 194 IRQ_TYPE_LEVEL_LOW>;
			ranges;
		};

		pcie@2,0 {
			reg = <0x1000 0 0 0 0>;
			#address-cells = <3>;
			#size-cells = <2>;
			#interrupt-cells = <1>;
			interrupt-map-mask = <0 0 0 0>;
			interrupt-map = <0 0 0 0 &sysirq GIC_SPI 195 IRQ_TYPE_LEVEL_LOW>;
			ranges;
		};
	};