gen/fhdl/hierarchy: Sort instances to generate deterministic hierarch…

…y in verilog.

litex/gen/fhdl/hierarchy.py

@@ -41,7 +41,7 @@ def get_tree(self, module, ident=0, with_modules=True, with_instances=True, with
                 r += self.get_tree(mod, ident + 1)
 
         # Instances.
-        for s in module._fragment.specials:
+        for s in sorted(module._fragment.specials, key=lambda x: str(x)):
             if (self.depth is None) or (ident <= self.depth):
                 if isinstance(s, Instance):
                     show = with_instances