dt-bindings: Move panel bindings to correct location

Device tree bindings for display panels have moved to a new location.
Unfortunately some of the new bindings added recently ended up in the
old location. Move them to their proper place.
Reported-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>