platform/vfs.c: add option path redirection

Optional for now, since not all games or configurations may need it.
It may be better eventually to refactor hooklib/path.c to allow for
static path remapping, to minimize boilerplate code around the functions.

platform/vfs.h

@@ -9,6 +9,7 @@ struct vfs_config {
     bool enable;
     wchar_t amfs[MAX_PATH];
     wchar_t appdata[MAX_PATH];
+    wchar_t option[MAX_PATH];
 };
 
 HRESULT vfs_hook_init(const struct vfs_config *config);