x86/mwait-idle: enable Ivy Bridge Xeon support

Matching a similar change in Linux 3.7-rc.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>

xen/arch/x86/cpu/mwait-idle.c

@@ -365,6 +365,7 @@ static struct intel_idle_id {
 	ICPU(0x2a, snb),
 	ICPU(0x2d, snb),
 	ICPU(0x3a, ivb),
+	ICPU(0x3e, ivb),
 	{}
 };