bus/megadrive/cart: initial pass at a new cart slot interface

[angelosa]

Hooked up to Teradrive only as WIP intermediate step.

List of improvements and changes compared to legacy handling (some of these also applies there):

• Implement gamenko Seganet mapper;
• Implement menghu mapper (a Gamtec variant using Z80 to read protection data);
• Implement sanguo5 / tunshi mapper (uses SRAM with invalid header);
• Implement sportg Tectoy 3-in-1 mapper;
• Hookup SRAM in yasech mapper;
• fix btlchess mapper;
• Implement 16mj2 extra ports reads;
• Fix sampras hanging on menu (uses a J-Cart variant);
• Hookup J-Cart for sskid;
• Allow ninjab to boot with proper I2C mapper;
• Fix I2C mappers for billwlsh, madden93, madd93ce, shanewar;
• sonic3 "fram" area doesn't exist anymore, use "sram" instead;
• Retire rom_radica from legacy handling: it has been moved as standalone sega/megadriv_rad.cpp driver starting from various reorganization of radica and vtech stuff #3108

machine/i2cmem: add 24C65 alias for bighurt/brianl96/collslam/shanewar [Angelo Salese, Happy]

New working software list items

megadriv: Nyuushi Chokuzen Check Nanmon Kimon Kiki Kaikai, Planet Message Quiz [Hidden Palace]

[angelosa]

Loop is:

1. go in options
2. edit teams
3. press 'C' -> create team
4. put whatever as name, press 'C' on player menu -> finished
5. press 'C' on team selection -> finished
6. (will have i2c activity on please wait screen)
7. exit emulation, reload with steps 1, 2. Check the created team is there at the end of list (concealed in Teradrive because this clearly needs a PAL machine).

Somehow megadriv still seems unhappy in its handler, probably the legacy implementation fumbles over?