x86: Correct wording of coreboot source code

Some files are taken or modified from coreboot, but the files are
no-longer part of the coreboot project. Fix the wording in a few places.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>

arch/x86/cpu/coreboot/timestamp.c

@@ -1,8 +1,8 @@
 // SPDX-License-Identifier: GPL-2.0+
 /*
- * This file is part of the coreboot project.
- *
  * Copyright (C) 2011 The ChromiumOS Authors.  All rights reserved.
+ *
+ * Modified from the coreboot version
  */
 
 #include <common.h>

arch/x86/include/asm/arch-coreboot/timestamp.h

@@ -1,8 +1,8 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * This file is part of the coreboot project.
- *
  * Copyright (C) 2011 The ChromiumOS Authors.  All rights reserved.
+ *
+ * Taken from the coreboot version
  */
 
 #ifndef __COREBOOT_TIMESTAMP_H__

arch/x86/include/asm/intel_pinctrl_defs.h

@@ -1,7 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * This file is part of the coreboot project.
- *
  * Copyright (C) 2015-2016 Intel Corp.
  * Copyright 2019 Google LLC
  *