Better encapsulation of Midway Zeus/Zeus 2 register spaces

[Hydreigon223]

• The whole offset based register issue is the same premise as this but applies to Midway Zeus and Zeus 2's video emulation. Log handling will likely need to be redone.
• williams/midzeus_v.cpp likely needs the devicification treatment.
• video/zeus2.cpp consists of not only per game hacks but a per driver hack, all of which need to be addressed.