The Aspeed System Control Unit manages the global behaviour of the SoC,
configuring elements such as clocks, pinmux, and reset.

Required properties:
- compatible:	One of:
		"aspeed,ast2400-scu", "syscon", "simple-mfd"
		"aspeed,ast2500-scu", "syscon", "simple-mfd"

- reg:		contains the offset and length of the SCU memory region
- #clock-cells: should be set to <1> - the system controller is also a
	clock provider
- #reset-cells: should be set to <1> - the system controller is also a
	reset line provider

Example:

syscon: syscon@1e6e2000 {
	compatible = "aspeed,ast2400-scu", "syscon", "simple-mfd";
	reg = <0x1e6e2000 0x1a8>;
	#clock-cells = <1>;
	#reset-cells = <1>;
};