>>fc417f+(OP)
A device tree is probably counted as data, so not copyrightable. I am not a lawyer and this is not legal advice. But there's plenty else that is GPL, and in AVM vs Sebastian Steck, it seems that even LGPLv2 requires the manufacturer to give you all the stuff you need to install a modified version of the software, i.e. it seems that all GPL licenses imply anti-tivoization.
That case was dismissed because they settled privately, so technically it does not prove anything about LGPLv2, and Germany is not as big on blindly following precedent in law as other countries anyway.