Refactor GetSubTree method

Since the GetSubTree method has been implemented in dbus_utility and
this commit is to integrate all the places where the GetSubTree
method is called, and use the method in dbus_utility uniformly.

Tested: Redfish Validator Passed

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: If3852b487d74e7cd8f123e0efffbd4affe92743c
diff --git a/redfish-core/lib/pcie_slots.hpp b/redfish-core/lib/pcie_slots.hpp
index d25b66b..1c4b6e9 100644
--- a/redfish-core/lib/pcie_slots.hpp
+++ b/redfish-core/lib/pcie_slots.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "app.hpp"
+#include "dbus_utility.hpp"
 #include "error_messages.hpp"
 #include "generated/enums/pcie_slot.hpp"
 #include "pcie.hpp"
@@ -9,9 +10,13 @@
 #include "utils/dbus_utils.hpp"
 #include "utils/json_utils.hpp"
 
+#include <boost/system/error_code.hpp>
 #include <sdbusplus/asio/property.hpp>
 #include <sdbusplus/unpack_properties.hpp>
 
+#include <array>
+#include <string_view>
+
 namespace redfish
 {
 
@@ -259,18 +264,15 @@
         return;
     }
 
-    crow::connections::systemBus->async_method_call(
+    constexpr std::array<std::string_view, 1> interfaces = {
+        "xyz.openbmc_project.Inventory.Item.PCIeSlot"};
+    dbus::utility::getSubTree(
+        "/xyz/openbmc_project/inventory", 0, interfaces,
         [asyncResp,
-         chassisID](const boost::system::error_code ec,
+         chassisID](const boost::system::error_code& ec,
                     const dbus::utility::MapperGetSubTreeResponse& subtree) {
         onMapperSubtreeDone(asyncResp, chassisID, ec, subtree);
-        },
-        "xyz.openbmc_project.ObjectMapper",
-        "/xyz/openbmc_project/object_mapper",
-        "xyz.openbmc_project.ObjectMapper", "GetSubTree",
-        "/xyz/openbmc_project/inventory", int32_t(0),
-        std::array<const char*, 1>{
-            "xyz.openbmc_project.Inventory.Item.PCIeSlot"});
+        });
 }
 
 inline void requestRoutesPCIeSlots(App& app)