dt-bindings: display: move ANX7814 and SiI8620 bridge bindings

A few bindings snuck into bindings/video/bridge since consolidating
everything under bindings/display/bridge/. Move them to the correct
spot.

Cc: Andrzej Hajda <a.hajda@samsung.com>
Acked-by: NThierry Reding <treding@nvidia.com>
Acked-by: NArchit Taneja <architt@codeaurora.org>
Acked-by: NEnric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: NRob Herring <robh@kernel.org>