legal: Add LICENSES directory with MSLA Snapshot to comply reuse

For the record the file has been snapshoted this way:

  mkdir -p LICENSES ;
  lynx -dump https://www.silabs.com/about-us/legal/master-software-license-agreement  \
  | tail +161 | head -n 842 | tee LICENSES/LicenseRef-MSL | sha256sum
  # 1cfe8601a36fbff16686cf84d36dbd20c4c691faa9c4672231ba2eefa6f37e1b  -

Origin: #16
Signed-off-by: Philippe Coval <[email protected]>

Author: rzr