arm64: dts: imx8mq: Add NWL MIPI DSI controller

Add a node for the Northwest Logic MIPI DSI IP core, "disabled" by
default. This also adds the necessary port to LCDIF.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Tested-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>