Test: Add build config which support level 3 isolation

Before this change only the core test suit was executed with level 3
isolation. From now regression test cases which compliant with
TFM_LVL 3 isolation can be executed with this setting.

Change-Id: Iddc376384583590cef4e47209b779f55d73ff41b
Signed-off-by: Tamas Ban <tamas.ban@arm.com>
diff --git a/ConfigRegression.cmake b/ConfigRegression.cmake
index 306d850..f0c80da 100755
--- a/ConfigRegression.cmake
+++ b/ConfigRegression.cmake
@@ -27,6 +27,9 @@
 set (REGRESSION True)
 set (CORE_TEST False)
 
+# TF-M isolation level: 1..3
+set (TFM_LVL 1)
+
 #BL2 bootloader(MCUBoot) related settings
 if(NOT DEFINED BL2)
 	set(BL2 True)