QTI Virtio SPMI controller (Virtio PMIC Arbiter)

The Virtio SPMI PMIC Arbiter is a frontend proxy based on backend virtio device.

Required properties:
- compatible : should be "qcom,viospmi-pmic-arb".
- #address-cells : must be set to 2
- #size-cells : must be set to 0
- interrupt-controller : boolean indicator that the PMIC arbiter is an interrupt controller
- #interrupt-cells :  must be set to 4. Interrupts are specified as a 4-tuple:
    cell 1: slave ID for the requested interrupt (0-15)
    cell 2: peripheral ID for requested interrupt (0-255)
    cell 3: the requested peripheral interrupt (0-7)
    cell 4: interrupt flags indicating level-sense information, as defined in
            dt-bindings/interrupt-controller/irq.h

Example Virtio PMIC-Arbiter:

     spmi_bus: qcom,spmi {
         compatible = "qcom,viospmi-pmic-arb";
         interrupt-names = "periph_irq";
         interrupts = <GIC_SPI 481 IRQ_TYPE_NONE>;
         qcom,ee = <0>;
         #address-cells = <2>;
         #size-cells = <0>;
         interrupt-controller;
         #interrupt-cells = <4>;
         cell-index = <0>;
     };

     viospmi: virtio-spmi@c440000 {
         compatible = "virtio,mmio";
         #address-cells = <1>;
         #size-cells = <1>;
         reg = <0xc440000 0x1100>;
         interrupts = <GIC_SPI 100 IRQ_TYPE_NONE>;
         status = "okay";
     };