dt-bindings: display: sitronix,st7701: document port and rotation

Panels are supposed to have one port (defined in panel-common.yaml
binding) and can have also rotation:

  rk3326-odroid-go3.dtb: panel@0: 'port', 'rotation' do 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>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Link: https://lore.kernel.org/r/20230326204224.80181-4-krzysztof.kozlowski@linaro.org
Signed-off-by: Rob Herring <robh@kernel.org>