Added the interface and the stubbs to update the PM config for the
devices. Sample code for the simulated OLT and ponsim will be provided
in a subsequent update.  Also deleted some commented out lines that were no longer
relevant to clean up the code a bit.

Change-Id: I8c7ba9a957ae2b7ba8ec816410bfb9ba01527625
diff --git a/voltha/adapters/broadcom_onu/broadcom_onu.py b/voltha/adapters/broadcom_onu/broadcom_onu.py
index 1854d32..3e96e1c 100644
--- a/voltha/adapters/broadcom_onu/broadcom_onu.py
+++ b/voltha/adapters/broadcom_onu/broadcom_onu.py
@@ -112,6 +112,9 @@
     def get_device_details(self, device):
         raise NotImplementedError()
 
+    def update_pm_config(self, device, pm_configs):
+        raise NotImplementedError()
+
     def update_flows_bulk(self, device, flows, groups):
         log.info('bulk-flow-update', device_id=device.id,
                   flows=flows, groups=groups)