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/audio_core/hle/dsp.cpp

@@ -0,0 +1,42 @@
+// Copyright 2016 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "audio_core/hle/dsp.h"
+#include "audio_core/hle/pipe.h"
+
+namespace DSP {
+namespace HLE {
+
+SharedMemory g_region0;
+SharedMemory g_region1;
+
+void Init() {
+    DSP::HLE::ResetPipes();
+}
+
+void Shutdown() {
+}
+
+bool Tick() {
+    return true;
+}
+
+SharedMemory& CurrentRegion() {
+    // The region with the higher frame counter is chosen unless there is wraparound.
+
+    if (g_region0.frame_counter == 0xFFFFu && g_region1.frame_counter != 0xFFFEu) {
+        // Wraparound has occured.
+        return g_region1;
+    }
+
+    if (g_region1.frame_counter == 0xFFFFu && g_region0.frame_counter != 0xFFFEu) {
+        // Wraparound has occured.
+        return g_region0;
+    }
+
+    return (g_region0.frame_counter > g_region1.frame_counter) ? g_region0 : g_region1;
+}
+
+} // namespace HLE
+} // namespace DSP