[yocto] a new layer that support spdx

[Lei, Maohui]

Hi all

I have submitted a new layer named meta-spdxscanner that can be used to create spdx files to the OpenEmbedded layer index.
Compared to the spdx module in oe-core, this layer has features as following:

  * Easy to use
    Dosocs2-native has been add into this meta, there is no need to install anything in build server.
  * Good performance
    It has better performance than the spdx module in current oe-core, especially in rebuilding.


Best regards
Lei Maohui