Platform: Enable multi-core test on PSoC 64

Set TFM_MULTI_CORE_TEST to ON in PSoC 64 cmake config file to
enable multi-core tests.

Change-Id: Id1e4cc138ffa89ec7daee692d0b9383d77fbc142
Signed-off-by: David Hu <david.hu@arm.com>
diff --git a/platform/ext/psoc64.cmake b/platform/ext/psoc64.cmake
index 066d70d..ec1287a 100644
--- a/platform/ext/psoc64.cmake
+++ b/platform/ext/psoc64.cmake
@@ -28,6 +28,10 @@
 
 # Skip peripheral access test
 set(TFM_ENABLE_PERIPH_ACCESS_TEST OFF)
+if (REGRESSION)
+    # Enable multi-core specific test cases
+    set(TFM_MULTI_CORE_TEST ON)
+endif()
 
 # Set Cortex-M0plus as secure core
 set_secure_cpu_type("CpuM0p")