s390x/ipl: always load the bios for ccw machine

s390x/ipl: always load the bios for ccw machine

We will need bios support in order to be able to support selecting a
different boot device via diagnose 308 in the ccw machine, so let's
make the bios mandatory for the ccw machine.

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Signed-off-by: Fan Zhang <zhangfan@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>