dt-bindings: display: add te-gpios to panel-common

Several bindings specifies a "te-gpios" for tearing effect signal.
Add this to panel-common so we have a shared definition.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200408195109.32692-4-sam@ravnborg.org

Documentation/devicetree/bindings/display/panel/panel-common.yaml

@@ -124,6 +124,13 @@ properties:
       while active. Active high reset signals can be supported by inverting the
       GPIO specifier polarity flag.
 
+  te-gpios:
+    maxItems: 1
+    description:
+      GPIO spec for the tearing effect synchronization signal.
+      The tearing effect signal is active high. Active low signals can be
+      supported by inverting the GPIO specifier polarity flag.
+
   # Power
   power-supply:
     description: