PCI: iproc: Add DT docs for Broadcom iProc PCIe driver

Document the Broadcom iProc PCIe platform interface device tree binding.
Signed-off-by: Ray Jui <rjui@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

Documentation/devicetree/bindings/pci/brcm,iproc-pcie.txt

+* Broadcom iProc PCIe controller with the platform bus interface
+
+Required properties:
+- compatible: Must be "brcm,iproc-pcie"
+- reg: base address and length of the PCIe controller I/O register space
+- #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
+- linux,pci-domain: PCI domain ID. Should be unique for each host controller
+- bus-range: PCI bus numbers covered
+- #address-cells: set to <3>
+- #size-cells: set to <2>
+- device_type: set to "pci"
+- ranges: ranges for the PCI memory and I/O regions
+
+Optional properties:
+- phys: phandle of the PCIe PHY device
+- phy-names: must be "pcie-phy"
+
+Example:
+	pcie0: pcie@18012000 {
+		compatible = "brcm,iproc-pcie";
+		reg = <0x18012000 0x1000>;
+
+		#interrupt-cells = <1>;
+		interrupt-map-mask = <0 0 0 0>;
+		interrupt-map = <0 0 0 0 &gic GIC_SPI 100 IRQ_TYPE_NONE>;
+
+		linux,pci-domain = <0>;
+
+		bus-range = <0x00 0xff>;
+
+		#address-cells = <3>;
+		#size-cells = <2>;
+		device_type = "pci";
+		ranges = <0x81000000 0 0	  0x28000000 0 0x00010000
+			  0x82000000 0 0x20000000 0x20000000 0 0x04000000>;
+
+		phys = <&phy 0 5>;
+		phy-names = "pcie-phy";
+	};
+
+	pcie1: pcie@18013000 {
+		compatible = "brcm,iproc-pcie";
+		reg = <0x18013000 0x1000>;
+
+		#interrupt-cells = <1>;
+		interrupt-map-mask = <0 0 0 0>;
+		interrupt-map = <0 0 0 0 &gic GIC_SPI 106 IRQ_TYPE_NONE>;
+
+		linux,pci-domain = <1>;
+
+		bus-range = <0x00 0xff>;
+
+		#address-cells = <3>;
+		#size-cells = <2>;
+		device_type = "pci";
+		ranges = <0x81000000 0 0	  0x48000000 0 0x00010000
+			  0x82000000 0 0x40000000 0x40000000 0 0x04000000>;
+
+		phys = <&phy 1 6>;
+		phy-names = "pcie-phy";
+	};