s390/futex: Avoid KMSAN instrumention for user pointers

Similar to commit eb6efdfe ("s390/uaccess: add KMSAN support to
put_user() and get_user()") disable KMSAN instrumention for futex inline
assemblies, which contain dereferenced user pointers. With KMSAN
instrumentation this would lead to accesses of shadows for user pointers,
which should not happen.

Handle the futex operations like they copy a value (old) from user
space to kernel space.

Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>