Squashed 'pothos-sdr/' content from commit b3d1276

git-subtree-dir: pothos-sdr
git-subtree-split: b3d127632ab5a04e30b3d08e9da85235e6f7e537
Merge commit '444601d3b5acc85543361a253b2404b2aa320ab1' as 'pothos-sdr'
pothos-sdr: added sdr blocks to the build