s390/sclp_vt220: Enable ASCII console per default

When you want to use the HMC's ASCII console as console device for
a z/VM guest you have to specify console=ttyS1 on the kernel command
line. But it won't work until you specify conmode=sclp as well.

This behavior is inconsistent with the use of the ASCII console as
TTY device which works on z/VM without the need to specify a conmode.

Fix this inconsistency by removing the check for conmode=sclp in the
ASCII console registration function.

Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>