MLK-25574-1 dt-bindings: display: bridge: nwl-dsi: Add compatible string for...

MLK-25574-1 dt-bindings: display: bridge: nwl-dsi: Add compatible string for i.MX8ulp DSI host controller

This patch adds compatible string for i.MX8ulp DSI host controller in
the DSI host controller's DT binding documentation.

Reviewed-by: Sandor Yu <Sandor.yu@nxp.com>
Signed-off-by: Liu Ying <victor.liu@nxp.com>