dt-bindings: display: samsung,s6d7aa0: Document port

dt-bindings: display: samsung,s6d7aa0: Document port

This MIPI-DSI LCD panel must be connected to something, thus add missing
port property, already used in DTS.  Reported by dtbs_check:

  qcom/msm8916-samsung-gt58.dtb: panel@0 (samsung,lsl080al03): 'port' does not match any of the regexes: '^pinctrl-[0-9]+$'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patch.msgid.link/20260306-dt-bindings-display-panel-clean-v1-1-3086eda1efaf@oss.qualcomm.com