banked: enhanced banked functions

[jorgegv]

The final goal is to free as much as possible low memory and make it available for game data.

Additional enhancements to the engine banked code:

• Generalize the function type definition to encode argument types and return type, so that any function can be migated to banked code. E.g. function type banked_function_a16_a16_r8_t for a type of function that receives two 16-bit arguments and returns a 8-bit value; banked_function_a16_t for a function that receives one 16-bit argument and returns nothing (void), etc.
• Create memory_call_banked_function_... functions for the different function types defined in the previous point.
• Migrate more functions to banked_code area so that in 128K mode more engine is in upper code banks. Appropriate new function types and memory_call_banked_function_... functions should be defined if needed to accomodate the args and return types of the migrated functions.

[jorgegv]

first 2 tasks done in 277a488