Moves the bulk of the code in the spdx-common bbclass into library code (From OE-Core rev: 3f9b7c7f6b15493b6890031190ca8d1a10f2f384) Signed-off-by: Joshua Watt <JPEWhacker@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>