Stop using DV to mean simulation #255

Part of lowRISC/dvplan#129.

DVSim uses DV to mean simulation in places, which stops working as soon as a formal flow is part of the same picture. DV covers both, and the bundle config added under lowRISC/dvplan#129 takes flow: dv for exactly that reason.

Scope

• Sweep the prose, docstrings, help text and log messages for DV used to mean simulation, and say simulation where simulation is meant. flow: sim keeps its name, since it does name a simulation.
• doc/dv_evidence.md needs care. The format name lowrisc-dv-evidence is written into files that already exist, so the name stays. What changes is the prose describing it as what a simulation flow writes, since a formal run can produce one too.
• Directory names such as hw/ip/<ip>/dv/ belong to OpenTitan and are out of scope.

Done when

• No user-facing string in DVSim uses DV to mean simulation.
• doc/dv_evidence.md describes a producer as a regression flow of any kind.