s390: add a few more SPDX identifiers

Add the correct SPDX license to a few more files under arch/s390 and
drivers/s390 which have been missed to far.
The SPDX identifier is a legally binding shorthand, which can be used
instead of the full boiler plate text.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/Kbuild

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
 generic-y += asm-offsets.h
 generic-y += cacheflush.h
 generic-y += clkdev.h

arch/s390/include/asm/alternative.h

@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _ASM_S390_ALTERNATIVE_H
 #define _ASM_S390_ALTERNATIVE_H
 

arch/s390/include/asm/ap.h

@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Adjunct processor (AP) interfaces
  *

arch/s390/include/asm/bugs.h

@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  *  S390 version
  *    Copyright IBM Corp. 1999

arch/s390/include/asm/segment.h

@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _ASM_SEGMENT_H
 #define _ASM_SEGMENT_H
 

arch/s390/include/asm/vga.h

@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _ASM_S390_VGA_H
 #define _ASM_S390_VGA_H