Binding for simple memory mapped io fixed-rate clock sources.
The driver reads a clock frequency value from a single 32-bit memory mapped
I/O register and registers it as a fixed rate clock.

It was designed for test systems, like FPGA, not for complete, finished SoCs.

This binding uses the common clock binding[1].

[1] Documentation/devicetree/bindings/clock/clock-bindings.txt

Required properties:
- compatible : shall be "fixed-mmio-clock".
- #clock-cells : from common clock binding; shall be set to 0.
- reg : Address and length of the clock value register set.

Optional properties:
- clock-output-names : From common clock binding.

Example:
sysclock: sysclock@fd020004 {
	#clock-cells = <0>;
	compatible = "fixed-mmio-clock";
	reg = <0xfd020004 0x4>;
};
