Enable tach signal handler

Register and handle tach change signals for each tach sensor.
Inventory would be updated when all tach sensors for a specific fan
enclosure have a tach value of zero.

Change-Id: Idd3f53c29c68c6171d858e616fbfe868f30a4ea9
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
diff --git a/fan_enclosure.hpp b/fan_enclosure.hpp
index 0b96bfc..5c6a040 100644
--- a/fan_enclosure.hpp
+++ b/fan_enclosure.hpp
@@ -32,6 +32,7 @@
             addInventory();
         }
 
+        void updInventory();
         void addSensor(
             std::unique_ptr<Sensor>&& sensor);