Save states do not save/restore MSU-1 status

[qwertymodo]

Loading a save state in a MSU-1 enabled game doesn't properly reload the MSU-1 state. Symptoms vary by game, but mostly it means you load your game with no background music playing.

[devinacker]

I assume higan works as expected, at least?

There's also a MSU-1 feature I've been meaning to finally backport - namely, the audio resume support that was added to the spec a few higan versions ago, so I'll probably tackle both of those things at the same time.

[qwertymodo]

Yes, higan works correctly. If you save a state and then load it, the MSU-1 audio gets reloaded along with everything else.