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>