namco/toypop.cpp: Use tilemap helpers, fixed save states, and cleaned up code: (#13101)

* Use tilemap helpers for tile maps.
* Register member variables for save states, and suppress side effects for debugger reads.
* Derive sound chip clock frequency from master crystal frequency.
* Simplified graphics decoding.
* Reduced run time tag lookups, reduced preprocessor macros, and made some variables const.

Author: cam900