dt-bindings: display/bridge: sil, sii9234: Convert to YAML binding

Convert the Silicon Image SiI9234 HDMI/MHL bridge documentation to YAML.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211006152158.601856-1-angelogioacchino.delregno@collabora.com