Reduce multiple oem_ibm entry points in pldmd

Abstract the custom method of `OEM-IBM` into the oem-ibm.hpp file
to prevent the continuous increase of custom code and reduce multiple
`OEM-IBM` entry points in pldmd.

Tested: enabled oem-ibm and built pldm successfully.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: Ieddb8d12281553e70bdb1c333bd29425c9d14fb0
diff --git a/libpldmresponder/platform.hpp b/libpldmresponder/platform.hpp
index 89eca61..b045d84 100644
--- a/libpldmresponder/platform.hpp
+++ b/libpldmresponder/platform.hpp
@@ -54,7 +54,6 @@
             pldm_pdr* repo, HostPDRHandler* hostPDRHandler,
             pldm::state_sensor::DbusToPLDMEvent* dbusToPLDMEventHandler,
             fru::Handler* fruHandler,
-            pldm::responder::oem_platform::Handler* oemPlatformHandler,
             pldm::responder::platform_config::Handler* platformConfigHandler,
             pldm::requester::Handler<pldm::requester::Request>* handler,
             sdeventplus::Event& event, bool buildPDRLazily = false,
@@ -63,10 +62,9 @@
         instanceIdDb(instanceIdDb), pdrRepo(repo),
         hostPDRHandler(hostPDRHandler),
         dbusToPLDMEventHandler(dbusToPLDMEventHandler), fruHandler(fruHandler),
-        dBusIntf(dBusIntf), oemPlatformHandler(oemPlatformHandler),
-        platformConfigHandler(platformConfigHandler), handler(handler),
-        event(event), pdrJsonDir(pdrJsonDir), pdrCreated(false),
-        pdrJsonsDir({pdrJsonDir})
+        dBusIntf(dBusIntf), platformConfigHandler(platformConfigHandler),
+        handler(handler), event(event), pdrJsonDir(pdrJsonDir),
+        pdrCreated(false), pdrJsonsDir({pdrJsonDir})
     {
         if (!buildPDRLazily)
         {
@@ -211,6 +209,16 @@
      */
     EventMap eventHandlers;
 
+    /* @brief Method to set the oem platform handler in platform handler class
+     *
+     * @param[in] handler - oem platform handler
+     */
+    inline void
+        setOemPlatformHandler(pldm::responder::oem_platform::Handler* handler)
+    {
+        oemPlatformHandler = handler;
+    }
+
     /** @brief Handler for GetPDR
      *
      *  @param[in] request - Request message payload
@@ -500,7 +508,7 @@
     pldm::state_sensor::DbusToPLDMEvent* dbusToPLDMEventHandler;
     fru::Handler* fruHandler;
     const pldm::utils::DBusHandler* dBusIntf;
-    pldm::responder::oem_platform::Handler* oemPlatformHandler;
+    pldm::responder::oem_platform::Handler* oemPlatformHandler = nullptr;
     pldm::responder::platform_config::Handler* platformConfigHandler;
     pldm::requester::Handler<pldm::requester::Request>* handler;
     sdeventplus::Event& event;