s390/sclp_tty: enable line mode tty even if there is an ascii console

commit 8f50af49 ("s390/console: Make preferred console handling
more consistent") created a separate console state for the ascii
console. This has the side effect that we register no tty for the line
mode interface as soon as there an ascii interface as default console.
Under KVM this results in no getty program on the line mode tty if the
guest has both types of interfaces.

As we can have multiple ttys at the same time we do not want to disable
the tty on sclp_line0 under KVM. So instead of checking for the console
mode, we now check for the presence of the sclp line mode interface. As
z/VM multiplexes the line mode interface on the 32xx screen we continue
to disable the line mode tty for the z/VM case.

CC: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Fixes: 8f50af49

 ("s390/console: Make preferred console handling more consistent")
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>