s390: require mvcos facility for z10 and newer machines

With inlined uaccess functions we always need the mvcos facility.
Checking at each inline place if mvcos is available would make the
inlining of get_user/put_user pointless.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>