Move DVDRead from DVDInterface to Boot

It was previously an important part of DVDInterface,
but since its usage there was replaced with DVDThread,
the only remaining uses of it are in Boot and Boot_BS2Emu.

Source/Core/Core/Boot/Boot.h

@@ -41,6 +41,7 @@ public:
 	                        std::string* title_id = nullptr);
 
 private:
+	static bool DVDRead(u64 dvd_offset, u32 output_address, u32 length, bool decrypt);
 	static void RunFunction(u32 _iAddr);
 
 	static void UpdateDebugger_MapLoaded();