media: dt-bindings: chrontel,ch7322: reference common CEC properties

Reference common HDMI CEC adapter properties to simplify the binding and
have only one place of definition for common properties.  The common CEC
binding expects also node name to be 'cec'.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>