x86: pvclock: Add flag to indicate that a vm was stopped by the host

This flag will be used to check if the vm was stopped by the host when a soft
lockup was detected.  The host will set the flag when it stops the guest.  On
resume, the guest will check this flag if a soft lockup is detected and skip
issuing the warning.

Signed-off-by: Eric B Munson <emunson@mgebm.net>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>