arm64: dts: verdin-imx8mm: introduce hdmi-connector

The Lontium LT8912B driver needs a HDMI connector to be connected to
port 1. Introduce this connector to be enabled in a device tree overlay.

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>