arm64: dts: renesas: white-hawk-cpu: Add DP output support

arm64: dts: renesas: white-hawk-cpu: Add DP output support

Add DT nodes needed for the mini DP connector. The DP is driven by
sn65dsi86, which in turn gets the pixel data from the SoC via DSI.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20221201095631.89448-6-tomi.valkeinen+renesas@ideasonboard.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>