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/common/logging/log.h

@@ -73,6 +73,8 @@ enum class Class : ClassType {
     Render,                     ///< Emulator video output and hardware acceleration
     Render_Software,            ///< Software renderer backend
     Render_OpenGL,              ///< OpenGL backend
+    Audio,                      ///< Emulator audio output
+    Audio_DSP,                  ///< The HLE implementation of the DSP
     Loader,                     ///< ROM loader
 
     Count ///< Total number of logging classes