drivers: Use SPDX identifiers

Convert the remaining files in src/drivers to use SPDX identifiers.

int15.h and default_brightness_levels.asl did not have license headers,
but they were both copied from other GPL2 files, so they should be under
the GPL2 as well.

ne2k.c and drm_dp_helper.h are licensed under custom BSD-like licenses
that do not have an SPDX equivalent, so they are added as exceptions
to the license header lint.

Change-Id: I87fb1c637b8d11b0463f7c19f70b847413e14aed
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41601
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/drivers/vpd/vpd_tables.h

@@ -1,10 +1,6 @@
-/*
- * Copyright (c) 2014 The Chromium OS Authors. All rights reserved.
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- *
- * Ported from mosys project (http://code.google.com/p/mosys/).
- */
+/* SPDX-License-Identifier: BSD-3-Clause */
+
+/* Ported from mosys project (http://code.google.com/p/mosys/). */
 
 #ifndef __LIB_VPD_TABLES_H__
 #define __LIB_VPD_TABLES_H__