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

Upstream commit 97291094 ("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>

arch/arm/boot/dts/qcom-apq8064-arrow-sd-600eval.dts

@@ -387,6 +387,11 @@ hdmi-tx@4a00000 {
 			hpd-gpio = <&tlmm_pinmux 72 GPIO_ACTIVE_HIGH>;
 
 			ports {
+				port@0 {
+					endpoint {
+						remote-endpoint = <&mdp_dtv_out>;
+					};
+				};
 				port@1 {
 					endpoint {
 						remote-endpoint = <&hdmi_con>;