i'm designing Libre Hardware, right now. i've been on this task for the past five years, since the embarrassing time when i encouraged 20 software libre developers to join me in buying one of the very first ARM netbooks to come out (back in 2010) that turned out to be GPL-violating.
So you have a GPL ARM netbook somewhere? Can you please provide me the URL to download the RTL for that ARM chip you have in that netbook? Also, please send me the URL to download the silicon layout files? Which foundry did you contract with to build that chip? TSMC?
All commercial contract silicon foundries with any semi-recent process node (32nm or lower) require you to sign an NDA before they provide you with the transistor models for their manufacturing process. If your ARM chip design is under a GPL license, how do you deal with the fact that it is impossible to distribute your layout file without also distributing the layout for your foundry's transistor design which is under NDA?
Even if your CPU design is fully synthesizable and you only distribute the RTL (which by the way will make your design a bit slower than if you had VLSI engineers custom design some of the critical paths in the CPU layout)... wouldn't running the synthesis tool be the same as running the compiler on software source code, so wouldn't the layout files that result from the synthesis be considered a derived work which also must be GPL licensed? Also, last time I checked there isn't any open source synthesis tools and both Synopsis and Cadence charge 6-figures to license their closed source synthesis tools. Are you addressing the lack of open source design tools? Do you have a cluster somewhere with some of that software available?
In other words... I'm 100% sure that your ARM silicon design is not GPL, in fact I'm 100% sure that it's not open source because ARM Limited Inc. only provides ARM licenses under NDA. You bought that ARM chip from some company with a closed source silicon design. The only thing you are focused on is designing an open source PCB to put a closed source CPU on top of. You make the incorrect assumption that just because you can send your PCB to any PCB manufacturer and get the same result back, the same thing can be applied to chips. PCBs are easy, chips are hard. The OP is right. There is a fundamental difference when you are talking about manufacturing something that requires billions of dollars worth of capital expense in order to create the factory necessary to build the device. Nobody spends billions to create the capability to manufacture modern silicon and then gives away their factory's transistor design in today's world. Until open source foundry exists and open source silicon design exists... your obsession over firmware binary blobs is penny wise and dollar dumb.
If you want to actually change something, you should be pitching open source foundry... honestly I think its a rather hard sell :) The much more feasible thing for you to do would be to start developing open source silicon design software. Just like how GCC was a prerequisite to an open source UNIX, open source silicon design tools are a prerequisite to open source hardware.