dt-bindings: display: Convert connectors to DT schema

Convert the analog TV, DVI, HDMI, and VGA connector bindings to DT schema
format.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200630200216.1172566-1-robh@kernel.org