ARM: dts: qcom-apq8064-arrow-sd-600eval fix graph_endpoint warning

ARM: dts: qcom-apq8064-arrow-sd-600eval fix graph_endpoint warning

BugLink: https://bugs.launchpad.net/bugs/1837257
Upstream commit 972910948fb6 ("ARM: dts: qcom: Remove Arrow SD600
eval board") removed this file because there are no known users,
but in linux-4.19.y, we still get a compile-time warnign for it:

arch/arm/boot/dts/qcom-apq8064-arrow-sd-600eval.dtb: Warning (graph_endpoint): /soc/mdp@5100000/ports/port@3/endpoint: graph connection to node '/soc/hdmi-tx@4a00000/ports/port@0/endpoint' is not bidirectional

Address the warning by adding the remote endpoint that makes the link
bidirectional. This is the same property that other boards use.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>