AudioCore: Skeleton Implementation

This commit:
* Adds a new subproject, audio_core.
* Defines structures that exist in DSP shared memory.
* Hooks up various other parts of the emulator into audio core.

This sets the foundation for a later HLE DSP implementation.

src/core/hle/service/dsp_dsp.h

@@ -23,7 +23,15 @@ public:
     }
 };
 
-/// Signals that a DSP interrupt has occurred to userland code
-void SignalInterrupt();
+/// Signal all audio related interrupts.
+void SignalAllInterrupts();
+
+/**
+ * Signal a specific audio related interrupt based on interrupt id and channel id.
+ * @param interrupt_id The interrupt id
+ * @param channel_id The channel id
+ * The significance of various values of interrupt_id and channel_id is not yet known.
+ */
+void SignalInterrupt(u32 interrupt_id, u32 channel_id);
 
 } // namespace