linux-wandboard

[S390] console: allow vt220 console to be the only console

Fix console detection logic to support configurations in which the
vt220 console is the only available Linux console.

Signed-off-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>