dt-bindings: media: meson-ao-cec: convert to yaml

Now that we have the DT validation in place, let's convert the device tree
bindings for the Amlogic AO-CEC controller over to a YAML schemas.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Rob Herring <robh@kernel.org>