media: dt-bindings: document the tegra CEC bindings

This documents the binding for the Tegra CEC module.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

Documentation/devicetree/bindings/media/tegra-cec.txt

+* Tegra HDMI CEC hardware
+
+The HDMI CEC module is present in Tegra SoCs and its purpose is to
+handle communication between HDMI connected devices over the CEC bus.
+
+Required properties:
+  - compatible : value should be one of the following:
+	"nvidia,tegra114-cec"
+	"nvidia,tegra124-cec"
+	"nvidia,tegra210-cec"
+  - reg : Physical base address of the IP registers and length of memory
+	  mapped region.
+  - interrupts : HDMI CEC interrupt number to the CPU.
+  - clocks : from common clock binding: handle to HDMI CEC clock.
+  - clock-names : from common clock binding: must contain "cec",
+		  corresponding to the entry in the clocks property.
+  - hdmi-phandle : phandle to the HDMI controller, see also cec.txt.
+
+Example:
+
+cec@70015000 {
+	compatible = "nvidia,tegra124-cec";
+	reg = <0x0 0x70015000 0x0 0x00001000>;
+	interrupts = <GIC_SPI 3 IRQ_TYPE_LEVEL_HIGH>;
+	clocks = <&tegra_car TEGRA124_CLK_CEC>;
+	clock-names = "cec";
+};