s390x: Add linemode console

z/VM isn't fond of vt220, so we need line mode when running under
z/VM.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20190920080356.1948-3-frankja@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>