Use a separate thread in test_codec, with the same (IRAM) stack as the main codec thread. Add a function to the plugin API to steal the codec thread, which test_codec copies and then restores. Now libmad can be benchmarked.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@13347 a1c6a512-1295-4272-9138-f99709370657

apps/plugin.c

@@ -493,6 +493,7 @@ static const struct plugin_api rockbox_api = {
     codec_load_file,
     get_metadata,
     get_codec_filename,
+    steal_codec_stack,
 #endif
 };