powerpc/boot: Convert more files to use SPDX tags

These files are all plain GPL 2.0, with a second sentence about being
licensed as-is.

Similar to the rule in commit 577b61cee5b2 ("treewide: Replace GPLv2
boilerplate/reference with SPDX - gpl-2.0_398.RULE").

Signed-off-by: Michael Ellerman <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/boot/44x.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * PowerPC 44x related functions
  *
  * Copyright 2007 David Gibson, IBM Corporation.
- *
- * This file is licensed under the terms of the GNU General Public
- * License version 2.  This program is licensed "as is" without any
- * warranty of any kind, whether express or implied.
  */
 #ifndef _PPC_BOOT_44X_H_
 #define _PPC_BOOT_44X_H_

arch/powerpc/boot/4xx.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * PowerPC 4xx related functions
  *
  * Copyright 2007 IBM Corporation.
  * Josh Boyer <[e-mail]>
- *
- * This file is licensed under the terms of the GNU General Public
- * License version 2.  This program is licensed "as is" without any
- * warranty of any kind, whether express or implied.
  */
 #ifndef _POWERPC_BOOT_4XX_H_
 #define _POWERPC_BOOT_4XX_H_

arch/powerpc/boot/ops.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Global definition of all the bootwrapper operations.
  *
  * Author: Mark A. Greer <[e-mail]>
  *
- * 2006 (c) MontaVista Software, Inc.  This file is licensed under
- * the terms of the GNU General Public License version 2.  This program
- * is licensed "as is" without any warranty of any kind, whether express
- * or implied.
+ * 2006 (c) MontaVista Software, Inc.
  */
 #ifndef _PPC_BOOT_OPS_H_
 #define _PPC_BOOT_OPS_H_

arch/powerpc/boot/serial.c

···
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Generic serial console support
  *
···
  * Code in serial_edit_cmdline() copied from <file:arch/ppc/boot/simple/misc.c>
  * and was written by Matt Porter <[e-mail]>.
  *
- * 2001,2006 (c) MontaVista Software, Inc.  This file is licensed under
- * the terms of the GNU General Public License version 2.  This program
- * is licensed "as is" without any warranty of any kind, whether express
- * or implied.
+ * 2001,2006 (c) MontaVista Software, Inc.
  */
 #include <stdarg.h>
 #include <stddef.h>

arch/powerpc/boot/simple_alloc.c

···
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Implement primitive realloc(3) functionality.
  *
  * Author: Mark A. Greer <[e-mail]>
  *
- * 2006 (c) MontaVista, Software, Inc.  This file is licensed under
- * the terms of the GNU General Public License version 2.  This program
- * is licensed "as is" without any warranty of any kind, whether express
- * or implied.
+ * 2006 (c) MontaVista, Software, Inc.
  */
 
 #include <stddef.h>