bmc-state: Add property signal for lastRebootTime

This sends the changedProperty signal for lastRebootTime when it is
updated via the timesync signal. It will allow us to use the correct
lastRebootTime instead of the pre-sync time.

Change-Id: I7c651e28de2bb3f2b86746e043dcaa2def0a6bc3
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/bmc_state_manager.cpp b/bmc_state_manager.cpp
index efaa0a2..22f2a42 100644
--- a/bmc_state_manager.cpp
+++ b/bmc_state_manager.cpp
@@ -254,6 +254,7 @@
     auto rebootTimeTs = now - seconds(info.uptime);
     rebootTime =
         duration_cast<milliseconds>(rebootTimeTs.time_since_epoch()).count();
+    server::BMC::lastRebootTime(rebootTime);
 }
 
 uint64_t BMC::lastRebootTime() const