[cleanup] Fix license checker after #11851

1. Exclude //third_party from license checks.
2. Add license headers to a few files.

Signed-off-by: Chris Frantz <cfrantz@google.com>

util/device_sw_utils/BUILD

diff --git a/util/device_sw_utils/BUILD b/util/device_sw_utils/BUILD
index 3895b01..63c648e 100644
--- a/util/device_sw_utils/BUILD
+++ b/util/device_sw_utils/BUILD
@@ -1,3 +1,7 @@
+# Copyright lowRISC contributors.
+# Licensed under the Apache License, Version 2.0, see LICENSE for details.
+# SPDX-License-Identifier: Apache-2.0
+
 load("@rules_python//python:defs.bzl", "py_binary")
 load("@ot_python_deps//:requirements.bzl", "requirement")
 

util/licence-checker.hjson

diff --git a/util/licence-checker.hjson b/util/licence-checker.hjson
index 4e4fe63..494da95 100644
--- a/util/licence-checker.hjson
+++ b/util/licence-checker.hjson
@@ -10,6 +10,7 @@
     ''',
   exclude_paths: [
     # Exclude anything in vendored directories
+    'third_party/**',
     '*/vendor/*/*',
     'util/lowrisc_misc-linters/*',