xen/x86: set panic notifier priority to minimum

Execution is not going to continue after telling Xen about the crash.
Let other panic notifiers run by postponing the final hypercall as much
as possible.
Signed-off-by: NAndrew Jones <drjones@redhat.com>
Signed-off-by: NRadim Krčmář <rkrcmar@redhat.com>
Signed-off-by: NDavid Vrabel <david.vrabel@citrix.com>

arch/x86/xen/enlighten.c

@@ -1339,6 +1339,7 @@ xen_panic_event(struct notifier_block *this, unsigned long event, void *ptr)
 
 static struct notifier_block xen_panic_block = {
 	.notifier_call= xen_panic_event,
+	.priority = INT_MIN
 };
 
 int xen_panic_handler_init(void)