KVM: s390: gaccess: simplify translation exception handling

The payload data for protection exceptions is a superset of the
payload of other translation exceptions. Let's set the additional
flags and use a fall through to minimize code duplication.

Signed-off-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>