Draft: di-tool: add a binary to dump the display info in YAML

Eventually the goal is to create EDID and DisplayID blobs from such a YAML file. For that we will also need serialization functions in the libdisplay-info library.

A few things to discuss:

• Should this be part of libdisplay-info?
• Should we create bindings for other languages and then build the utilities on that? I'm not that happy with having to use C here.
• If sticking to C: there is an event API in libyaml that can be used to output YAML without having to build a tree. Might be a better fit.
• generic di-tool/di-util or specific di-yaml binary?
• are there other/better yaml parser/emitters?
• Instead of writing code for each struct and field can we describe how to serialize them instead?
• anything else, really