Listener:Present property callback stub

This commit adds APIs in Listener to register "Present" property change
callback for all FRUs for which vpd-manager does not handle presence and
which are hot pluggable. If such a FRU is plugged in/removed,
vpd-manager needs to detect this and collect/delete the VPD of the FRU.
Note: this is a stub implementation, and actual implementation will be
handled in future commit(s).

Change-Id: Ib7edc633bc6395976f2f3d1e4b3c5f90a6b999bc
Signed-off-by: Souvik Roy <souvikroyofficial10@gmail.com>
diff --git a/vpd-manager/oem-handler/ibm_handler.cpp b/vpd-manager/oem-handler/ibm_handler.cpp
index 293837f..45e8759 100644
--- a/vpd-manager/oem-handler/ibm_handler.cpp
+++ b/vpd-manager/oem-handler/ibm_handler.cpp
@@ -62,6 +62,7 @@
     m_eventListener = std::make_shared<Listener>(m_worker, m_asioConnection);
     m_eventListener->registerAssetTagChangeCallback();
     m_eventListener->registerHostStateChangeCallback();
+    m_eventListener->registerPresenceChangeCallback();
 
     // set async timer to detect if system VPD is published on D-Bus.
     SetTimerToDetectSVPDOnDbus();