dt-bindings: adi,adv7511.txt: document cec clock

- adi,disable-timing-generator: Only for ADV7533. Disables the internal timing

  generator. The chip will rely on the sync signals in the DSI data lanes,

  rather than generate its own timings for HDMI output.

- clocks: from common clock binding: reference to the CEC clock.

- clock-names: from common clock binding: must be "cec".

Required nodes:

		reg = <39>;

		interrupt-parent = <&gpio3>;

		interrupts = <29 IRQ_TYPE_EDGE_FALLING>;

		clocks = <&cec_clock>;

		clock-names = "cec";

		adi,input-depth = <8>;

		adi,input-colorspace = "rgb";