ARM: dts: iwg20d-q7-dbcm-ca: Add HDMI video output

Although there is a HDMI connector on the q7 carrier board it is not
connected to the RZ/G1M SoC. One must use the HDMI connector on the
camera daughter board.

This patch adds support for this connector.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>