[S390] Fix smsgiucv init on no iucv machines

smsgiucv is a driver that relies on iucv to work properly. If
iucv ans smsgiucv are compiled into the kernel and run on an
lpar the following scenario happens:
iucv is initialized early as a subsystem. It checks for z/VM and
returns with EPROTONOTSUPPORT. Later smsgiucv tries to run
driver_register with iucv_bus as bus. As this bus is not
initialized the driver core and list debugging issue several
warnings and oopses.

Solution is to let smsgiucv also check for z/VM and return
EPROTONOTSUPPORT as well.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>