seta/ssv.cpp: Cleanups and modernizations (#12349)

* seta/ssv.cpp: Cleanups and modernizations
 - Split driver state class for with DSP
- Use C++ style comments for single line comments
- Suppress side effects for debugger read
- Reduce preprocessor defines
- Reduce duplicate
- Fix spacing
- Reduce unnecessary lines
- Constantize variables
- Fix typename values
- Fix document
- Reduce usage of literal tags
- Reduce runtime tag lookup
- Use generic gfx decode layout for gdfs tilemap
- Fix naming for ROM region and tags

Author: cam900