KVM: s390: epoch difference and TOD programmable field

This patch makes vcpu epoch difference and the TOD programmable
field accessible from userspace. This is needed in order to
implement a couple of instructions that deal with the time of
day clock on s390, such as SET CLOCK and for migration.

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>