Core: Remove some header inclusions in header files

Replaces them with forward declarations of used types, or removes them entirely if they aren't used at all. This also replaces certain Common headers with less inclusive ones (in terms of definitions they pull in).

Source/Core/Core/DSP/DSPIntExtOps.h

@@ -25,7 +25,7 @@
 
 #pragma once
 
-#include "Core/DSP/DSPTables.h"
+#include "Core/DSP/DSPCommon.h"
 
 // Extended opcode support.
 // Many opcode have the lower 0xFF (some only 0x7f) free - there, an opcode extension