Realtek XB2 Controller

Required properties:
- compatible: "realtek,rts3903-xb2"
- reg: Address range of the XB2 registers
- interrupt: Should contain the XB2 interrupt number
- interrupt-parent: Should be the phandle for the interrupt controller
  that services interrupts for this device

Example:

	xb2: xb2@0x18870000 {
		compatible = "realtek,rts3903-xb2";
		reg = <0x18870000 0x30>;
		interrupts = <BSP_IRQ_OTHERS>;
		interrupt-parent = <&cpuintc>;
	};
