System: Add option to use a single memory card for playlists

src/core/system.h

@@ -108,6 +108,9 @@ bool HasMedia();
 bool InsertMedia(const char* path);
 void RemoveMedia();
 
+/// Returns true if a playlist is being used.
+bool HasMediaPlaylist();
+
 /// Returns the number of entries in the media/disc playlist.
 u32 GetMediaPlaylistCount();