sblaster/ymf262: save state fixes

[moralrecordings]

• Sound Blaster now saves DSP registers to the state
• Fixed an issue where Sound Blaster DAC would create loud popping noises before first use (the uninitialized DAC would hold at -1, which during a dropped frame would step to 0?)
• Adlib chip now saves channel/slot info to the state. Part of that involved saving the slot connection routes in a non-raw pointer format so they can be reconstituted at runtime. Also, pointer validity checks!