sched-host-tran: add base interfaces for Scheduled Host Transition

Implement interfaces to get/set scheduledTime and requestedTransition.

Tested:
1. Check scheduledTime
 # busctl get-property xyz.openbmc_project.State.ScheduledHostTransition \
   /xyz/openbmc_project/state/host0 \
   xyz.openbmc_project.State.ScheduledHostTransition ScheduledTime
   t 0
 # busctl set-property xyz.openbmc_project.State.ScheduledHostTransition \
   /xyz/openbmc_project/state/host0 \
   xyz.openbmc_project.State.ScheduledHostTransition ScheduledTime t 1
 # busctl get-property xyz.openbmc_project.State.ScheduledHostTransition \
   /xyz/openbmc_project/state/host0 \
   xyz.openbmc_project.State.ScheduledHostTransition ScheduledTime
   t 1
2. Check requestedTransition
 # busctl get-property xyz.openbmc_project.State.ScheduledHostTransition \
   /xyz/openbmc_project/state/host0 \
   xyz.openbmc_project.State.ScheduledHostTransition RequestedTransition
   s "xyz.openbmc_project.State.Host.Transition.On"
 # busctl set-property xyz.openbmc_project.State.ScheduledHostTransition \
   /xyz/openbmc_project/state/host0 \
   xyz.openbmc_project.State.ScheduledHostTransition RequestedTransition \
   s "xyz.openbmc_project.State.Host.Transition.Off"
 # busctl get-property xyz.openbmc_project.State.ScheduledHostTransition \
   /xyz/openbmc_project/state/host0 \
   xyz.openbmc_project.State.ScheduledHostTransition RequestedTransition
   s "xyz.openbmc_project.State.Host.Transition.Off"

Change-Id: Ie7da8034d37c1069db043772f35982ca821826ae
Signed-off-by: Carol Wang <wangkair@cn.ibm.com>
diff --git a/scheduled_host_transition.hpp b/scheduled_host_transition.hpp
new file mode 100644
index 0000000..ebf3fba
--- /dev/null
+++ b/scheduled_host_transition.hpp
@@ -0,0 +1,44 @@
+#pragma once
+
+#include <sdbusplus/bus.hpp>
+#include <phosphor-logging/log.hpp>
+#include <xyz/openbmc_project/State/ScheduledHostTransition/server.hpp>
+
+namespace phosphor
+{
+namespace state
+{
+namespace manager
+{
+
+using ScheduledHostTransitionInherit = sdbusplus::server::object::object<
+    sdbusplus::xyz::openbmc_project::State::server::ScheduledHostTransition>;
+
+/** @class ScheduledHostTransition
+ *  @brief Scheduled host transition implementation.
+ *  @details A concrete implementation for
+ *  xyz.openbmc_project.State.ScheduledHostTransition
+ */
+class ScheduledHostTransition : public ScheduledHostTransitionInherit
+{
+  public:
+    ScheduledHostTransition(sdbusplus::bus::bus& bus, const char* objPath) :
+        ScheduledHostTransitionInherit(bus, objPath)
+    {
+    }
+
+    ~ScheduledHostTransition() = default;
+
+    /**
+     * @brief Handle with scheduled time
+     *
+     * @param[in] value - The seconds since epoch
+     * @return The time for the transition. It is the same as the input value if
+     * it is set successfully. Otherwise, it won't return value, but throw an
+     * error.
+     **/
+    uint64_t scheduledTime(uint64_t value) override;
+};
+} // namespace manager
+} // namespace state
+} // namespace phosphor
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