doc: add copyright/license header to doc scripts

Tracked-On: #5113

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/scripts/filter-known-issues.py

@@ -1,4 +1,6 @@
 #! /usr/bin/env python3
+# Copyright (c) 2017, Intel Corporation
+# SPDX-License-Identifier: Apache-2.0
 """
 Filters a file, classifying output in errors, warnings and discarding
 the rest.

doc/scripts/genrest.py

@@ -1,3 +1,5 @@
+# Copyright (c) 2017, Intel Corporation
+# SPDX-License-Identifier: Apache-2.0
 # Generates a Kconfig symbol reference in RST format, with a separate
 # CONFIG_FOO.rst file for each symbol, and an alphabetical index with links in
 # index.rst.