ptp_kvm: probe for kvm guest availability

ptp_kvm: probe for kvm guest availability

commit 001f60e1f662a6dee1630a2915401aaf5959d479 upstream.

In the event of moving pvclock_pvti_cpu0_va() definition to common
pvclock code, this function would return a value on non KVM guests.
Later on this would fail with a GPF on ptp_kvm_init when running on a
Xen guest. Therefore, ptp_kvm_init() should check whether it is running
in a KVM guest.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Acked-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>