coresight: document the bindings for the ATCLK

	* reg: physical base address and length of the register

	  set(s) of the component.

	* clocks: the clock associated to this component.

	* clock-names: the name of the clock as referenced by the code.

	  Since we are using the AMBA framework, the name should be

	  "apb_pclk".

	* clocks: the clocks associated to this component.

	* clock-names: the name of the clocks referenced by the code.

	  Since we are using the AMBA framework, the name of the clock

	  providing the interconnect should be "apb_pclk", and some

	  coresight blocks also have an additional clock "atclk", which

	  clocks the core of that coresight component. The latter clock

	  is optional.

	* port or ports: The representation of the component's port

	  layout using the generic DT graph presentation found in