dt-bindings: display: boe,tv101wum-nl6: document rotation

Allow 'rotation' property (coming from panel-common.yaml) already used
in DTS:

  sc7180-trogdor-quackingstick-r0.dtb: panel@0: 'rotation' does not match any of the regexes: 'pinctrl-[0-9]+'
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20230326155425.91181-6-krzysztof.kozlowski@linaro.orgSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/display/panel/boe,tv101wum-nl6.yaml

@@ -55,6 +55,7 @@ properties:
     description: phandle of the backlight device attached to the panel
 
   port: true
+  rotation: true
 
 required:
   - compatible