Update TF-M Profile Small config

Implement Profile Small config as a standalone one.
Enable SFN model in the config.

Change-Id: I9537eba248e0cfc03f981273d5d47d58f1b693d7
Signed-off-by: David Hu <david.hu@arm.com>
diff --git a/tfm_ci_pylib/tfm_build_manager.py b/tfm_ci_pylib/tfm_build_manager.py
index fc463ba..17dd9bd 100644
--- a/tfm_ci_pylib/tfm_build_manager.py
+++ b/tfm_ci_pylib/tfm_build_manager.py
@@ -78,7 +78,8 @@
                                     "-DCONFIG_TFM_LAZY_STACKING=OFF "),
                   "FVP":           "-DPLATFORM_IS_FVP=True",
                   "FPGA":          "-DPLATFORM_IS_FVP=False",
-                  "CC_DRIVER_PSA": "-DCC312_LEGACY_DRIVER_API_ENABLED=OFF"
+                  "CC_DRIVER_PSA": "-DCC312_LEGACY_DRIVER_API_ENABLED=OFF",
+                  "SFN_ENABLE":    "-DCONFIG_TFM_SPM_BACKEND=SFN"
                   }
 
 class TFM_Build_Manager(structuredTask):