rtio: Tracing

[teburd]

Is your enhancement proposal related to a problem? Please describe.
Tracing is a very useful feature to understand time ordering and latency issues. Being able to trace I/O related worked through RTIO would be a valuable feature that could be reused by all RTIO devices.

Describe the solution you'd like
Provide hooks and implementations to trace RTIO submission and completion pairs as if they are tasks in themselves. These can then be visualized in a tracing tool to see when submissions start and are completed over a time scale.