freertos: Add Copyright and License in flavour samples/files for reuse compliance

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

flavours/freertos/conf-notes.txt.license

+# SPDX-FileCopyrightText: Huawei Inc.
+#
+# SPDX-License-Identifier: Apache-2.0

flavours/freertos/local.conf.sample

+# SPDX-FileCopyrightText: Huawei Inc.
+#
+# SPDX-License-Identifier: Apache-2.0
+
 #
 # This file is your local configuration file and is where all local user settings
 # are placed. The comments in this file give some guide to the options a new user