dt-bindings: display/bridge: ptn3460: Convert to YAML binding

Convert the NXP PTN3460 eDP to LVDS 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/20211007075822.62411-1-angelogioacchino.delregno@collabora.com