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

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

flavours/linux/bblayers.conf.sample

+# SPDX-FileCopyrightText: Huawei Inc.
+#
+# SPDX-License-Identifier: Apache-2.0
+
 # POKY_BBLAYERS_CONF_VERSION is increased each time build/conf/bblayers.conf
 # changes incompatibly
 POKY_BBLAYERS_CONF_VERSION = "2"

flavours/linux/conf-notes.txt.license

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

flavours/linux/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