[media] dt-bindings: media: stm32 cec driver

Add bindings documentation for stm32 CEC driver.
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/devicetree/bindings/media/st,stm32-cec.txt

+STMicroelectronics STM32 CEC driver
+
+Required properties:
+ - compatible : value should be "st,stm32-cec"
+ - reg : Physical base address of the IP registers and length of memory
+	 mapped region.
+ - clocks : from common clock binding: handle to CEC clocks
+ - clock-names : from common clock binding: must be "cec" and "hdmi-cec".
+ - interrupts : CEC interrupt number to the CPU.
+
+Example for stm32f746:
+
+cec: cec@40006c00 {
+	compatible = "st,stm32-cec";
+	reg = <0x40006C00 0x400>;
+	interrupts = <94>;
+	clocks = <&rcc 0 STM32F7_APB1_CLOCK(CEC)>, <&rcc 1 CLK_HDMI_CEC>;
+	clock-names = "cec", "hdmi-cec";
+};