Introduce s390_guarded_storage system call decoder

Introduce s390_guarded_storage system call decoder

* linux/s390/syscallent.h ([378]): Change decoder to s390_guarded_storage.
* linux/s390x/syscallent.h: Likewise.
* s390.c (struct guard_storage_control_block,
struct guard_storage_event_parameter_list): New structure type
definition.
(guard_storage_print_gsepl, guard_storage_print_gscb,
SYS_FUNC(s390_guarded_storage)): New function.
(DIV_ROUND_UP): New macro.
* xlat/s390_guarded_storage_commands.in: New file.