CPU Backends: Make each CPU backend responsible for initializing its own

instruction tables

Previously, all of the internals that handled how the instruction tables
are initialized were exposed externally. However, this can all be made
private to each CPU backend.

If each backend has an Init() function, then this is where the instruction
tables should be initialized, it shouldn't be the responsibility of
external code to ensure internal validity.

This allows for getting rid of all the table initialization shenanigans
within JitInterface and PPCTables.

Source/Core/Core/PowerPC/JitInterface.h

@@ -22,7 +22,6 @@ enum class ExceptionType
 void DoState(PointerWrap& p);
 
 CPUCoreBase* InitJitCore(int core);
-void InitTables(int core);
 CPUCoreBase* GetCore();
 
 // Debugging