s390: add support for IBM zBC12 machine

commit 594712276e737961d30e11eae80d403b2b3815df upstream.

Just add the new model number where appropiate.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>