Add WiiSaveBanner class

This class is similar to the BannerLoaderWii class that was
removed in ee694e32.

Source/Core/DiscIO/CMakeLists.txt

@@ -18,6 +18,7 @@ set(SRCS
   VolumeGC.cpp
   VolumeWad.cpp
   VolumeWii.cpp
+  WiiSaveBanner.cpp
   WiiWad.cpp
 )