s390/kvm: Support for get/set of extended TOD-Clock for guest

s390/kvm: Support for get/set of extended TOD-Clock for guest

Provides an interface for getting and setting the guest's extended
TOD-Clock via a single ioctl to kvm. If the ioctl fails because it
is not support by kvm, then we fall back to the old style of
retrieving the clock via two ioctls.

Signed-off-by: Collin L. Walling <walling@linux.vnet.ibm.com>
Reviewed-by: Eric Farman <farman@linux.vnet.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
[split failure change from epoch index change]
Message-Id: <20171004105751.24655-2-borntraeger@de.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
[some cosmetic fixes]