dt-bindings: display: lt9611: Support single Port B input

dt-bindings: display: lt9611: Support single Port B input

The LT9611 has two DSI input ports (Port A and Port B). Update the
binding to clearly document the port mapping and allow using Port B
alone when DSI is physically connected to Port B only.

Changes:
- Clarify port@0 corresponds to DSI Port A input
- Clarify port@1 corresponds to DSI Port B input
- Change port requirement from mandatory port@0 to anyOf port@0/port@1,
  allowing either port to be used independently

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Hongyang Zhao <hongyang.zhao@thundersoft.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Roger Shimizu <rosh@debian.org>
Tested-by: Roger Shimizu <rosh@debian.org>
Link: https://patch.msgid.link/20260207-rubikpi-next-20260116-v3-1-23b9aa189a3a@thundersoft.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>