Use unique_ptr for sd_event object wrapper

Convert the sd_event object wrapper from a shared_ptr to
a unique_ptr.  Requires a new header file.

Change-Id: I868a9e88ed93878c2e0bb12e58f8d3a604510da0
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/monitor/tach_sensor.hpp b/monitor/tach_sensor.hpp
index 7a65b64..84e02fe 100644
--- a/monitor/tach_sensor.hpp
+++ b/monitor/tach_sensor.hpp
@@ -3,6 +3,7 @@
 #include <chrono>
 #include <sdbusplus/bus.hpp>
 #include <sdbusplus/server.hpp>
+#include "event.hpp"
 #include "timer.hpp"
 
 namespace phosphor
@@ -54,7 +55,7 @@
                    const std::string& id,
                    bool hasTarget,
                    size_t timeout,
-                   std::shared_ptr<sd_event>& events);
+                   phosphor::fan::event::EventPtr& events);
 
         /**
          * @brief Returns the target speed value