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/test/libpldmresponder_base_test.cpp b/libpldmresponder/test/libpldmresponder_base_test.cpp
index b1ca89d..0387209 100644
--- a/libpldmresponder/test/libpldmresponder_base_test.cpp
+++ b/libpldmresponder/test/libpldmresponder_base_test.cpp
@@ -28,7 +28,7 @@
     auto request = reinterpret_cast<pldm_msg*>(requestPayload.data());
     // payload length will be 0 in this case
     size_t requestPayloadLength = 0;
-    base::Handler handler(event, nullptr);
+    base::Handler handler(event);
     auto response = handler.getPLDMTypes(request, requestPayloadLength);
     // Need to support OEM type.
     auto responsePtr = reinterpret_cast<pldm_msg*>(response.data());
@@ -45,7 +45,7 @@
         requestPayload{};
     auto request = reinterpret_cast<pldm_msg*>(requestPayload.data());
     size_t requestPayloadLength = requestPayload.size() - sizeof(pldm_msg_hdr);
-    base::Handler handler(event, nullptr);
+    base::Handler handler(event);
     auto response = handler.getPLDMCommands(request, requestPayloadLength);
     auto responsePtr = reinterpret_cast<pldm_msg*>(response.data());
     uint8_t* payload_ptr = responsePtr->payload;
@@ -62,7 +62,7 @@
 
     request->payload[0] = 0xFF;
     size_t requestPayloadLength = requestPayload.size() - sizeof(pldm_msg_hdr);
-    base::Handler handler(event, nullptr);
+    base::Handler handler(event);
     auto response = handler.getPLDMCommands(request, requestPayloadLength);
     auto responsePtr = reinterpret_cast<pldm_msg*>(response.data());
     uint8_t* payload_ptr = responsePtr->payload;
@@ -87,7 +87,7 @@
 
     ASSERT_EQ(0, rc);
 
-    base::Handler handler(event, nullptr);
+    base::Handler handler(event);
     auto response = handler.getPLDMVersion(request, requestPayloadLength);
     auto responsePtr = reinterpret_cast<pldm_msg*>(response.data());
 
@@ -118,7 +118,7 @@
 
     ASSERT_EQ(0, rc);
 
-    base::Handler handler(event, nullptr);
+    base::Handler handler(event);
     auto response = handler.getPLDMVersion(request, requestPayloadLength - 1);
     auto responsePtr = reinterpret_cast<pldm_msg*>(response.data());
 
@@ -143,7 +143,8 @@
     auto request = reinterpret_cast<pldm_msg*>(requestPayload.data());
     size_t requestPayloadLength = 0;
 
-    base::Handler handler(event, nullptr);
+    base::Handler handler(event);
+    handler.setOemPlatformHandler(nullptr);
     auto response = handler.getTID(request, requestPayloadLength);
 
     auto responsePtr = reinterpret_cast<pldm_msg*>(response.data());