License
Update of the VHDL guidelines to include SPDX identifiers as done in : https://ohwr.org/project/spec/blob/master/hdl/top/golden/spec_golden.vhd
- Addition of the following lines on the header: https://ohwr.org/project/spec/blob/master/hdl/top/golden/spec_golden.vhd#L2
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-- SPDX-FileCopyrightText: 2020 CERN (home.cern)
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-- SPDX-License-Identifier: CERN-OHL-W-2.0+
- Addition of a folder LICENSES on the top of the repo structure: https://ohwr.org/project/spec/tree/master