Implement part of BmcEpoch

Add BmcEpoch which inherits EpochBase and will handle times for BMC,
it is partly implemented.

Add unit test cases to test basic functions.

Change-Id: Ia5e4d0f884156d238f3f84df490a2efbce43e89a
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/main.cpp b/main.cpp
index 0cf2807..05ac453 100644
--- a/main.cpp
+++ b/main.cpp
@@ -1,10 +1,12 @@
 #include <sdbusplus/bus.hpp>
 
 #include "config.h"
+#include "bmc_epoch.hpp"
 
 int main()
 {
     auto bus = sdbusplus::bus::new_default();
+    phosphor::time::BmcEpoch bmc(bus, OBJPATH_BMC);
 
     bus.request_name(BUSNAME);