dt-bindings: Add CDTech S043WQ26H-CT7 panel bindings

Add documentation for S043WQ26H-CT7 panel
Signed-off-by: NGiulio Benetti <giulio.benetti@micronovasrl.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NThierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180730231117.5631-6-giulio.benetti@micronovasrl.com

Documentation/devicetree/bindings/display/panel/cdtech,s043wq26h-ct7.txt

+CDTech(H.K.) Electronics Limited 4.3" 480x272 color TFT-LCD panel
+
+Required properties:
+- compatible: should be "cdtech,s043wq26h-ct7"
+- power-supply: as specified in the base binding
+
+Optional properties:
+- backlight: as specified in the base binding
+- enable-gpios: as specified in the base binding
+
+This binding is compatible with the simple-panel binding, which is specified
+in simple-panel.txt in this directory.