arm64: dts: rockchip: Enable HDMI receiver on rock-5b

The Rock 5B has a Micro HDMI port, which can be used for receiving
HDMI data. This enables support for it.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>