ARM: dts: da850-lcdk: add the vga-bridge node

Add the vga-bridge node to the board DT together with corresponding
ports and vga connector. This allows to retrieve the edid info from
the display automatically.

Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>