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/CMakeLists.txt

@@ -4,6 +4,7 @@ include_directories(.)
 add_subdirectory(common)
 add_subdirectory(core)
 add_subdirectory(video_core)
+add_subdirectory(audio_core)
 if (ENABLE_GLFW)
     add_subdirectory(citra)
 endif()