lantiq: fix console print for additional boards

I missed 3 boards in this commit:
commit d8dde8c517
Author: Hauke Mehrtens <hauke@hauke-m.de>
Date:   Wed Jan 4 21:53:22 2017 +0100

    lantiq: fix console print

Add bootargs parameters for ARV4525PW, ARV7506PW11 and ARV8539PW22
again.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/lantiq/dts/ARV4525PW.dts

@@ -7,6 +7,10 @@
 / {
 	model = "ARV4525PW - Speedport W501V Typ A";
 
+	chosen {
+		bootargs = "console=ttyLTQ0,115200";
+	};
+
 	aliases {
 		/* we dont have a power led, lets use the online led */
 		led-boot = &online;

target/linux/lantiq/dts/ARV7506PW11.dts

@@ -7,6 +7,10 @@
 / {
 	model = "ARV7506PW11 - Alice/O2 IAD 4421";
 
+	chosen {
+		bootargs = "console=ttyLTQ0,115200";
+	};
+
 	aliases {
 		led-boot = &power;
 		led-failsafe = &power_red;

target/linux/lantiq/dts/ARV8539PW22.dts

@@ -7,6 +7,10 @@
 / {
 	model = "ARV8539PW22 - Speedport W 504V Typ A";
 
+	chosen {
+		bootargs = "console=ttyLTQ0,115200";
+	};
+
 	aliases {
 		led-boot = &power_green;
 		led-failsafe = &power_red;