dt-bindings: Add CDTech S043WQ26H-CT7 panel bindings

Add documentation for S043WQ26H-CT7 panel

Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180730231117.5631-6-giulio.benetti@micronovasrl.com