Implement continuous vibration and AST

[mackieks]

Description:
Continuous vibration and AST (auto-stop time) is the last part of Dreamcast Purupuru spec left to implement. I tried a naïve implementation of BlockWriting AST at some point last year, but it didn't work as expected. This might fix a variety of rumble-related bugs in retail SW.

To-do:

• Use Colton's Purupuru tester homebrew add link to cdi here to refresh my memory on how this functionality works.
• Verify I can store AST data when the DC sends it via BlockWrite
• Does the DC ever read back AST data with BlockRead? I bet CE games do... need to implement this
• Verify AST works to end continuous vibration