KVM: SVM: Set the 'busy' flag of the TR selector

(cherry picked from c0d09828)

The busy flag of the TR selector is not set by the hardware. This breaks
migration from amd hosts to intel hosts.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>