dt-bindings: arm: msm: add initial devicetree documenation for MSI

* MSM PCIe MSI controller

=========

Main node

=========

- compatible:

	Usage: required

	Value type: <stringlist>

	Definition: Value to identify this is a MSM PCIe MSI controller

- msi-controller:

	Usage: required

	Value type: <bool>

	Definition: Indicates that this is a MSM PCIe MSI controller node

- reg:

	Usage: required

	Value type: <prop-encoded-array>

	Definition: Physical QGIC address (0x17a00040), MSI message address

- interrupt-parent:

	Usage: required

	Value type: <phandle>

	Definition: Phandle of the interrupt controller that services

		interrupts for this device

- interrupts:

	Usage: required

	Value type: <prop-encoded-array>

	Definition: Array of tuples which describe interrupt lines for PCIe MSI

=======

Example

=======

pcie0_msi: qcom,pcie0_msi {

	compatible = "qcom,pci-msi";

	msi-controller;

	reg = <0x17a10040 0x0 0x0 0x0 0xff>;

	interrupt-parent = <&intc>;

	interrupts = <GIC_SPI 832 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 833 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 834 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 835 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 836 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 837 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 838 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 839 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 840 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 841 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 842 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 843 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 844 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 845 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 846 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 847 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 848 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 849 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 850 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 851 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 852 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 853 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 854 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 855 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 856 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 857 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 858 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 859 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 860 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 861 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 862 IRQ_TYPE_EDGE_RISING>,

		<GIC_SPI 863 IRQ_TYPE_EDGE_RISING>;

};