Merge cflog and ftrace instrumentation

[surovic]

As this was a proof of concept at the time it was written I figured it was easier to create a new one. We weren't really sure what changes we needed. For now, it will allow us to integrate it without breaking anything else. Over time I think the functionality should be merged/unified.

Originally posted by @hbrodin in #6553 (comment)

Both instrumentations currently log function entry and exit. cflog seems to do more on top.