Build: Use Ninja based build

Ninja based build helps to improve build job performance.
A single build-config job takes ~52s for building TF-M.
A Ninja based build takes ~42s.

Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
Change-Id: I956b85bda93f51e0cbef6ea099b1a56e5c2686fd
diff --git a/build_helper/build_helper_configs.py b/build_helper/build_helper_configs.py
index 5a611b4..13271d6 100755
--- a/build_helper/build_helper_configs.py
+++ b/build_helper/build_helper_configs.py
@@ -48,7 +48,7 @@
     # Keys for the templace will come from the combinations of parameters
     # provided in the seed dictionary.
 
-    "config_template": "cmake " + \
+    "config_template": "cmake -G Ninja " + \
         "-DTFM_PLATFORM=%(tfm_platform)s " + \
         "-DTFM_TOOLCHAIN_FILE=%(codebase_root_dir)s/%(toolchain_file)s " + \
         "-DTFM_LIB_MODEL=%(lib_model)s " + \