FFmpegDL: Added external_dlls folder to user folder

AACDecoder: addressed reviews

src/common/common_paths.h

@@ -38,6 +38,7 @@
 #define SYSDATA_DIR "sysdata"
 #define LOG_DIR "log"
 #define CHEATS_DIR "cheats"
+#define DLL_DIR "external_dlls"
 
 // Filenames
 // Files in the directory returned by GetUserPath(UserPath::LogDir)

src/common/file_util.cpp

@@ -711,6 +711,7 @@ const std::string& GetUserPath(UserPath path, const std::string& new_path) {
         // TODO: Put the logs in a better location for each OS
         paths.emplace(UserPath::LogDir, user_path + LOG_DIR DIR_SEP);
         paths.emplace(UserPath::CheatsDir, user_path + CHEATS_DIR DIR_SEP);
+        paths.emplace(UserPath::DLLDir, user_path + DLL_DIR DIR_SEP);
     }
 
     if (!new_path.empty()) {

src/common/file_util.h

@@ -24,6 +24,7 @@ enum class UserPath {
     CacheDir,
     CheatsDir,
     ConfigDir,
+    DLLDir,
     LogDir,
     NANDDir,
     RootDir,