tco: add trace events

Add trace events to the PCH watchdog timer, it can be useful to see how
the guest is using it.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1507816448-86665-1-git-send-email-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>