* Clock bindings for Axis ARTPEC-6 chip

The bindings are based on the clock provider binding in
Documentation/devicetree/bindings/clock/clock-bindings.txt

External clocks:
----------------

There are two external inputs to the main clock controller which should be
provided using the common clock bindings.
- "sys_refclk": External 50 Mhz oscillator (required)
- "i2s_refclk": Alternate audio reference clock (optional).

Main clock controller
---------------------

Required properties:
- #clock-cells: Should be <1>
  See dt-bindings/clock/axis,artpec6-clkctrl.h for the list of valid identifiers.
- compatible: Should be "axis,artpec6-clkctrl"
- reg: Must contain the base address and length of the system controller
- clocks:  Must contain a phandle entry for each clock in clock-names
- clock-names: Must include the external oscillator ("sys_refclk"). Optional
  ones are the audio reference clock ("i2s_refclk") and the audio fractional
  dividers ("frac_clk0" and "frac_clk1").

Examples:

ext_clk: ext_clk {
	#clock-cells = <0>;
	compatible = "fixed-clock";
	clock-frequency = <50000000>;
};

clkctrl: clkctrl@f8000000 {
	#clock-cells = <1>;
	compatible = "axis,artpec6-clkctrl";
	reg = <0xf8000000 0x48>;
	clocks = <&ext_clk>;
	clock-names = "sys_refclk";
};
