xml: Sort the output tags.

```xml
<pb_type>
 <clocks by name/>
 <inputs by name/>
 <outputs by name/>
 <pb_type by name>
   ...
 </pb_type>
 <interconnect>
  <direct|mux by output>
 </interconnect>
</pb_type>
```

Signed-off-by: Tim 'mithro' Ansell <me@mith.ro>