target-i386: fix IvyBridge xlevel in PC_COMPAT_2_3

Previous patch changed xlevel and missed the compatibility code.

Fixes: 3046bb5d ("target-i386: emulate CPUID level of real hardware")
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>