s390/config: do not select VIRTIO_CONSOLE via Kconfig

select does not ensure that dependencies are also selected. Instead of
selecting VIRTIO_CONSOLE from S390_GUEST we should rather add this to
the defconfigs. So we update those as well.

Reported-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>