WiiRoot: Move content manipulation to separate functions

{Initialize,Shutdown}WiiRoot should only be responsible for setting the
SESSION_WII_ROOT or managing the temporary NAND directory.

Move all the content manipulation out of these functions to ensure
separation of concerns and call them after/before WiiRoot init/shutdown
to make sure they operate on the correct root.

Source/Core/Core/WiiRoot.h

@@ -8,4 +8,8 @@ namespace Core
 {
 void InitializeWiiRoot(bool use_temporary);
 void ShutdownWiiRoot();
+
+// Initialize or clean up the filesystem contents.
+void InitializeWiiFileSystemContents();
+void CleanUpWiiFileSystemContents();
 }