Add logs to stage1

[tiziano88]

There is room for improvement, but I want to get something in to debug other issues, and also to have some precedent in the code for other people to then add more logs and improve on.

Ref #4652

[andrisaar]

A fair chunk of these definitely aren't relevant most of the time, and thus should be only debug logs.

It's not like we have a way how to filter these (as at this stage all messages get dumped to the serial console), but could we use the log (or tracing) crate to set the log levels properly, even if we always print everything?