[PCB] update license to OHLv2-W
Update the license of the 3x PCBs from OHLv1.2 to OHLv2-W. As Javier explains "the PCB files seem to be copyright CERN and licensed under CERN OHL v1.2. It would be good to update them to CERN OHL v2, which means we need to choose a variant. For the PCBs, the W variant would allow us to cater for the fact that the KiCad libs might be proprietary or under some other open-source licencing regime, yet still benefit from improvements in the PCB design."
"Copyright CERN 2020. License under OHLv2-W.
This source describes Open Hardware and is licensed under the CERN-OHLW v2 You may redistribute and modify this documentation and make products using it under the terms of the CERN-OHL-W v2 (https:/cern.ch/cern-ohl). This documentation is distributed WITHOUT ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING OF MERCHANTABILITY, SATISFACTORY QUALITY AND FITNESS FOR A PARTICULAR PURPOSE. Please see the CERN-OHL-W v2 for applicable conditions."