s390/setup: diag 318: refactor struct

The diag 318 struct introduced in include/asm/diag.h can be
reused in KVM, so let's condense the version code fields in the
diag318_info struct for easier usage and simplify it until we
can determine how the data should be formatted.

Signed-off-by: Collin Walling <walling@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20200622154636.5499-2-walling@linux.ibm.com


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