Better encapsulation of various Voodoo I/O spaces

[angelosa]

• Voodoo(s) I/O space is really a switch-case hell with [[fallthrough]];, device id checks and offset-based register areas. A typical case where having progressive inheritance can help with readability and maintenance.
• PCI space is very stub, needs to be separated for each variant type;
• Voodoo Banshee/Voodoo 3 VGA portion should use the common architecture instead of reinventing the wheel;
• Voodoo Rush support cfr. ProMotion cards

[angelosa]

Break down OP message into tasks.