[U-Boot] DM, Kconfig and clang changes

Hey all,

So the release is out, and I want to make sure that some of these big changes get as much testing as we can.

Simon, can you please make up a pull request with what you think is ready to go now?

Masahiro and Jeroen, can you please make sure patchwork is up to date and perhaps setup a bundle with your changes that are ready (and for clang, not ARM centric, I want Albert to pick those up when he's ready, I'll review/comment tho).

Thanks!