Massive refactoring of all code + audio skeleton.

This should make it easier to find files and (in the future) split things
up into separate libraries.
It also changes around emulator initialization to make it a little more
difficult to do things out of order and a little more sensible as to when
real init work happens.
Also adding a skeleton audio system/driver and reworking CPU register
access to be more extensible.

src/xenia/cpu/jit.h

@@ -30,8 +30,8 @@ public:
   }
 
   virtual int Setup() = 0;
-  virtual void SetupGpuPointers(void* gpu_this,
-                                void* gpu_read, void* gpu_write) = 0;
+  virtual void AddRegisterAccessCallbacks(
+      ppc::RegisterAccessCallbacks callbacks) = 0;
 
   virtual int InitModule(ExecModule* module) = 0;
   virtual int UninitModule(ExecModule* module) = 0;