dt-bindings: display: anx7814.txt: convert to yaml

This converts the Analogix ANX7814 bridge DT binding to yaml. Port
definitions and descriptions were expanded, apart from that it's a
direct translation from the original binding.

Signed-off-by: Ricardo Cañuelo <ricardo.canuelo@collabora.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>