dt-bindings: display: Augment s6e63m0 bindings

This fixes the following problems with the s6e63m0 display
bindings:

- When used on the DSI bus, the panel is listed directly as
  a subnode on the DSI host so the "port" node is not
  compulsory. Remove "port" from required properties.

- The panel contains its own backlight control, so reference
  the backlight common properties and list default-brightness
  and max-brightness as supported but optional properties.

Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210101114522.1981838-1-linus.walleij@linaro.org

Documentation/devicetree/bindings/display/panel/samsung,s6e63m0.yaml

@@ -11,6 +11,7 @@ maintainers:
 
 allOf:
   - $ref: panel-common.yaml#
+  - $ref: /schemas/leds/backlight/common.yaml#
 
 properties:
   compatible:
@@ -19,6 +20,8 @@ properties:
   reg: true
   reset-gpios: true
   port: true
+  default-brightness: true
+  max-brightness: true
 
   vdd3-supply:
     description: VDD regulator
@@ -31,7 +34,6 @@ required:
   - reset-gpios
   - vdd3-supply
   - vci-supply
-  - port
 
 unevaluatedProperties: false