PCI: rcar: Add R-Car PCIe device tree bindings

* Renesas RCar PCIe interface

Required properties:

- compatible: should contain one of the following

	"renesas,pcie-r8a7779", "renesas,pcie-r8a7790", "renesas,pcie-r8a7791"

- reg: base address and length of the pcie controller registers.

- #address-cells: set to <3>

- #size-cells: set to <2>

- bus-range: PCI bus numbers covered

- device_type: set to "pci"

- ranges: ranges for the PCI memory and I/O regions.

- dma-ranges: ranges for the inbound memory regions.

- interrupts: two interrupt sources for MSI interrupts, followed by interrupt

	source for hardware related interrupts (e.g. link speed change).

- #interrupt-cells: set to <1>

- interrupt-map-mask and interrupt-map: standard PCI properties

	to define the mapping of the PCIe interface to interrupt

	numbers.

- clocks: from common clock binding: clock specifiers for the PCIe controller

	and PCIe bus clocks.

- clock-names: from common clock binding: should be "pcie" and "pcie_bus".

Example:

SoC specific DT Entry:

	pcie: pcie@fe000000 {

		compatible = "renesas,pcie-r8a7791";

		reg = <0 0xfe000000 0 0x80000>;

		#address-cells = <3>;

		#size-cells = <2>;

		bus-range = <0x00 0xff>;

		device_type = "pci";

		ranges = <0x01000000 0 0x00000000 0 0xfe100000 0 0x00100000

			  0x02000000 0 0xfe200000 0 0xfe200000 0 0x00200000

			  0x02000000 0 0x30000000 0 0x30000000 0 0x08000000

			  0x42000000 0 0x38000000 0 0x38000000 0 0x08000000>;

		dma-ranges = <0x42000000 0 0x40000000 0 0x40000000 0 0x40000000

			      0x42000000 2 0x00000000 2 0x00000000 0 0x40000000>;

		interrupts = <0 116 4>, <0 117 4>, <0 118 4>;

		#interrupt-cells = <1>;

		interrupt-map-mask = <0 0 0 0>;

		interrupt-map = <0 0 0 0 &gic 0 116 4>;

		clocks = <&mstp3_clks R8A7791_CLK_PCIE>, <&pcie_bus_clk>;

		clock-names = "pcie", "pcie_bus";

		status = "disabled";

	};