KVM: Use CONFIG_PREEMPT_NOTIFIERS around struct preempt_notifier

This allows kvm_host.h to be #included even when struct preempt_notifier is
undefined. This is needed to build ppc asm-offsets.h.
Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

include/linux/kvm_host.h

@@ -67,7 +67,9 @@ void kvm_io_bus_register_dev(struct kvm_io_bus *bus,
 
 struct kvm_vcpu {
 	struct kvm *kvm;
+#ifdef CONFIG_PREEMPT_NOTIFIERS
 	struct preempt_notifier preempt_notifier;
+#endif
 	int vcpu_id;
 	struct mutex mutex;
 	int   cpu;