Build: Disable CORE test for IPC model

Core test is enabled in reference board while regression is set. Disable
core test in this case due to some items are not ready for working under
IPC model and cause test errors (TFM_CORE_TEST_1007 e.g.).

Change-Id: I4fbfead047fe873be9b732fc7253885c234e7685
Signed-off-by: Edison Ai <edison.ai@arm.com>
diff --git a/CommonConfig.cmake b/CommonConfig.cmake
index 711b078..eb49a41 100644
--- a/CommonConfig.cmake
+++ b/CommonConfig.cmake
@@ -133,7 +133,7 @@
 if (SERVICES_TEST_ENABLED)
 	set(SERVICE_TEST_S ON)
 	set(SERVICE_TEST_NS ON)
-	if (REFERENCE_PLATFORM)
+	if (REFERENCE_PLATFORM AND NOT CORE_IPC)
 		set(CORE_TEST_POSITIVE ON)
 	endif()
 endif()