Use `m_` for all variable classes, but not for local/internal variables. [lexical guidelines]

[antmarzam]

Reason: When debugging code it becomes obvious which variables are internal to tasks/functions VS which ones are class variables.

[marnovandermaas]

How much code churn would this cause? I'm not convinced it makes sense to mandate this.

[antmarzam]

I agree, I was thinking more along the lines of suggesting it and trying to move our codebase to be more like this over time.

I don't know, currently AFAIK this is not common at all in Opentitan