Sandbox SPMI emulated arbiter.

This is bus driver for Sandbox. It includes part of emulated pm8916 pmic.

Required properties:
- compatible: "sandbox,spmi"
- #address-cells: 0x1 - childs slave ID address
- #size-cells: 0x1

Example:

spmi: spmi@0 {
	compatible = "sandbox,spmi";
	#address-cells = <0x1>;
	#size-cells = <0x1>;
	pm8916@0 {
		compatible = "qcom,spmi-pmic";
		reg = <0x0 0x1>;
		#address-cells = <0x1>;
		#size-cells = <0x1>;

		spmi_gpios: gpios@c000 {
			compatible = "qcom,pm8916-gpio";
			reg = <0xc000 0x400>;
			gpio-controller;
			gpio-count = <4>;
			#gpio-cells = <2>;
			gpio-bank-name="spmi";
		};
	};
};