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/tools/gen_opcode_table.c

@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Generate opcode table initializers for the in-kernel disassembler.
  *