arm64: dts: meson-g12a-u200: Add support for Video Display

This patch adds the HDMI, CVBS and CEC attributes and nodes to support
full display on the U200 Reference Design.

AO-CEC-B is used by default and AO-CEC-A is disabled.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>