these fixes: 1. add cross and native bootloader builders 2. add an option to specify which dtbs to copy over https://github.com/illegalprime/nixpkgs/commit/118faa3e8b04b5f874f5dcf1438c75565f9a3cbd https://github.com/illegalprime/nixpkgs/commit/f737bb01d9276314ff95c4e2a30fb478d9fd4caf
