ARM: dts: imx6qdl: Add IPU DI ports and endpoints, move imx-drm node to dtsi

This patch connects IPU and display encoder (HDMI, LVDS, MIPI)
device tree nodes, as well as parallel displays on the DISP0
and DISP1 outputs, using the OF graph bindings described in
Documentation/devicetree/bindings/media/video-interfaces.txt

The IPU ports correspond to the two display interfaces. The
order of endpoints in the ports is arbitrary.

Each encoder with an associated input multiplexer has multiple
input ports in the device tree. The order and reg property of
the ports must correspond to the multiplexer input order.

Since the imx-drm node now only needs to contain links to the
display interfaces, it can be moved to the SoC dtsi level. At
the board level, only connections between the display interface
ports and encoders or panels have to be added.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>