audio_core/hle: Stub binary requests SaveState and LoadState.

[Steveice10]

When the AAC decoder is being used, it hooks into the DSP sleep/wake behavior to send the following commands:

• Sleep: SaveState -> Shutdown
• Wake: Initialize -> LoadState

This implements stubs for SaveState and LoadState, currently doing nothing and returning a success response. Additionally, we now signal the binary interrupt when we finish a request; otherwise, games may hang waiting for completion.

This allows AAC games to suspend and resume to/from home menu without freezing, although resuming will break the current AAC audio since they aren't actually implemented yet.

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This change is