update BootProgressLastUpdate when BootProgress is set

Per the boot-progress.md[1] design document, the BootProgressLastUpdate
property should be updated with the current time since epoch in
microseconds whenever the BootProgress property is updated.

Tested:
- Confirmed that when BootProgress is updated, the
  BootProgressLastUpdate was updated with the correct time

[1]: https://github.com/openbmc/docs/blob/master/designs/boot-progress.md

Change-Id: I96bc1b03441e14dbb23bb5d175fc480fa25a1d52
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/host_state_manager.hpp b/host_state_manager.hpp
index 6bf4f94..5314a56 100644
--- a/host_state_manager.hpp
+++ b/host_state_manager.hpp
@@ -95,6 +95,9 @@
     /** @brief Set Value for boot progress */
     ProgressStages bootProgress(ProgressStages value) override;
 
+    /** @brief Updated whenever BootProgress is updated */
+    uint64_t bootProgressLastUpdate(uint64_t value) override;
+
     /** @brief Set Value for Operating System Status */
     OSStatus operatingSystemState(OSStatus value) override;