It is possible to build u-boot as the bios for qemux86, however it currently fails with the error: | unable to execute 'swig': No such file or directory | error: command 'swig' failed with exit status 1
I think I have the patches to fix this and will post them to the mailing list
http://lists.openembedded.org/pipermail/openembedded-core/2018-July/153590.html
in build
Fixed in: b91562697d1d04fb7cad15c1ab7d7bf3cd178589