DSP: Eliminate most global state

An unfortunately large single commit that deglobalizes the DSP code.
(which I'm very sorry about).

This would have otherwise been extremely difficult to separate due to
extensive use of the globals in very coupling ways that would result in
more scaffolding to work around than is worth it.

Aside from the video code, I believe only the DSP code is the hairiest
to deal with in terms of globals, so I guess it's best to get this dealt
with right off the bat.

A summary of what this commit does:
  - Turns the DSPInterpreter into its own class
    This is the most involved portion of this change.
    The bulk of the changes are turning non-member functions into member
    functions that would be situated into the Interpreter class.

  - Eliminates all usages to globals within DSPCore.
    This generally involves turning a lot of non-member functions into
    member functions that are either situated within SDSP or DSPCore.

  - Discards DSPDebugInterface (it wasn't hooked up to anything,
    and for the sake of eliminating global state, I'd rather get rid of
    it than think up ways for this class to be integrated with
    everything else.

  - Readjusts the DSP JIT to handle calling out to member functions.
    In most cases, this just means wrapping respective member function
    calles into thunk functions.

Surprisingly, this doesn't even make use of the introduced System class.
It was possible all along to do this without it. We can house everything
within the DSPLLE class, which is quite nice =)

Source/Core/Core/State.cpp

@@ -74,7 +74,7 @@ static Common::Event g_compressAndDumpStateSyncEvent;
 static std::thread g_save_thread;
 
 // Don't forget to increase this after doing changes on the savestate system
-constexpr u32 STATE_VERSION = 125;  // Last changed in PR 8867
+constexpr u32 STATE_VERSION = 126;  // Last changed in PR 9348
 
 // Maps savestate versions to Dolphin versions.
 // Versions after 42 don't need to be added to this list,