KVM: s390: introduce defines for control registers

In KVM code we use masks to test/set control registers.

Let's define the ones we use in arch/s390/include/asm/ctl_reg.h and
replace all occurrences in KVM code.

As we will be needing the define for Clock-comparator sign control soon,
let's also add it.

Suggested-by: Collin L. Walling <walling@linux.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Collin Walling <walling@linux.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>