logging_util: support to tweak loglevel directed to stderr/stdout

Previously we set loglevel >= WARNING printed to stderr and
loglevel < WARNING printed to stdout. To be more flexible, we
replace this `WARNING` value with an argument: split_level and leave
`WARNING` as default split_level if not set.

Signed-off-by: Yanray Wang <yanray.wang@arm.com>
diff --git a/scripts/code_size_compare.py b/scripts/code_size_compare.py
index 72c69e4..672b803 100755
--- a/scripts/code_size_compare.py
+++ b/scripts/code_size_compare.py
@@ -906,11 +906,8 @@
     comp_args = parser.parse_args()
 
     logger = logging.getLogger()
-    logging_util.configure_logger(logger)
-    if comp_args.stdout and not comp_args.verbose:
-        logger.setLevel(logging.ERROR)
-    else:
-        logger.setLevel(logging.DEBUG if comp_args.verbose else logging.INFO)
+    logging_util.configure_logger(logger, split_level=logging.NOTSET)
+    logger.setLevel(logging.DEBUG if comp_args.verbose else logging.INFO)
 
     if os.path.isfile(comp_args.record_dir):
         logger.error("record directory: {} is not a directory"