ARM: dts: omap: fix OF graph in omap3-devkit8000

omap3-devkit8000-common.dtsi defines a graph connection for DVI, but
then omap3-devkit8000-lcd-common.dtsi overrides that with a graph
connection for the LCD as the same output signals are used. This
leaves an incomplete graph as the TFP410 output has only half a
connection. The result is the following warning:

arch/arm/boot/dts/omap3-devkit8000-lcd70.dtb: Warning (graph_endpoint):
/encoder0/ports/port@0/endpoint: graph connection to node
'/ocp@68000000/dss@48050000/port/endpoint' is not bidirectional

Fix this by defining multiple endpoints which is the correct way to show
a 1 to many connection.

Cc: "Benoît Cousson" <bcousson@baylibre.com>
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>