Update PicoDrive

Future humans: Our super old copy of PicoDrive is checked-in to this repo. Upstream repo is https://github.com/notaz/picodrive, though development happens on https://github.com/irixxxx/picodrive. Original request follows. --yoshi

Libretro's PicoDrive is a pretty accurate core, but BizHawk's PicoDrive is a lot of steps down. I mean, just force BizHawk to load the official TiTAN Overdrive demo with BizHawk's PicoDrive with File Extensions window, and you see an unbelievably huge difference. Same accuracy as DGen! How is it that bad!? Did you port this from the first release of the PicoDrive!?

Now, believe me, you can get a lot better result of TiTAN Overdrive 2 in PicoDrive thanks to "Accurate" renderer.
There are some issues with savestates and audio, though.

I mean, just look at the video showing how PicoDrive can handle TiTAN Overdrive 2 to see what I am talking about (sorry for bad resolution):

https://drive.google.com/file/d/1IHDOPcB2JKY4eTmnWZYy2BuZwyOuhkhu/view?usp=sharing

Start by locating BizHawk's checked-in PicoDrive copy and comparing it with the upstream repositories linked in the issue. Review the reported renderer, savestate, and audio differences, then determine a specific update scope and verification cases before attempting the work.