lantiq: use soc_vendor_device scheme on DTS file

This renames lantiq DTS(I) files to follow soc_vendor_device scheme.
This will make DTS files easier to maintain.

As a side effect, DTS file name can be derived from device node
names now, only having to specify a SOC variable in Makefiles.

While at it, move files to arch/mips/boot/dts/lantiq subfolder.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/lantiq/files/arch/mips/boot/dts/DGN3500.dts → target/linux/lantiq/files/arch/mips/boot/dts/lantiq/ar9_netgear_dgn3500.dts

 /dts-v1/;
 
-#include "DGN3500.dtsi"
+#include "ar9_netgear_dgn3500.dtsi"
 
 / {
 	compatible = "netgear,dgn3500", "lantiq,xway", "lantiq,ar9";

target/linux/lantiq/files/arch/mips/boot/dts/DGN3500B.dts → target/linux/lantiq/files/arch/mips/boot/dts/lantiq/ar9_netgear_dgn3500b.dts

 /dts-v1/;
 
-#include "DGN3500.dtsi"
+#include "ar9_netgear_dgn3500.dtsi"
 
 / {
 	compatible = "netgear,dgn3500b", "lantiq,xway", "lantiq,ar9";

target/linux/lantiq/files/arch/mips/boot/dts/ARV4518PWR01.dts → target/linux/lantiq/files/arch/mips/boot/dts/lantiq/danube_arcadyan_arv4518pwr01.dts

 /dts-v1/;
 
-#include "ARV4518PWR01.dtsi"
+#include "danube_arcadyan_arv4518pwr01.dtsi"
 
 / {
 	compatible = "arcadyan,arv4518pwr01", "lantiq,xway", "lantiq,danube";

target/linux/lantiq/files/arch/mips/boot/dts/ARV4518PWR01A.dts → target/linux/lantiq/files/arch/mips/boot/dts/lantiq/danube_arcadyan_arv4518pwr01a.dts

 /dts-v1/;
 
-#include "ARV4518PWR01.dtsi"
+#include "danube_arcadyan_arv4518pwr01.dtsi"
 
 / {
 	compatible = "arcadyan,arv4518pwr01a", "lantiq,xway", "lantiq,danube";