s390x: add s390_sthyi system call from v4.15

to store hypervisor information, added in linux commit
3d8757b87d7fc15a87928bc970f060bc9c6dc618

arch/s390x/bits/syscall.h.in

@@ -322,4 +322,5 @@
 #define __NR_pwritev2                   377
 #define __NR_s390_guarded_storage       378
 #define __NR_statx                      379
+#define __NR_s390_sthyi                 380