KVM: PPC: fix kvmppc_start_thread() for CONFIG_SMP=N

Currently kvmppc_start_thread() tries to wake other SMT threads via
xics_wake_cpu().  Unfortunately xics_wake_cpu only exists when
CONFIG_SMP=Y so when compiling with CONFIG_SMP=N we get:

  arch/powerpc/kvm/built-in.o: In function `.kvmppc_start_thread':
  book3s_hv.c:(.text+0xa1e0): undefined reference to `.xics_wake_cpu'

The following should be fine since kvmppc_start_thread() shouldn't
called to start non-zero threads when SMP=N since threads_per_core=1.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/book3s_hv.c

@@ -538,7 +538,7 @@ static void kvmppc_start_thread(struct kvm_vcpu *vcpu)
 	tpaca->kvm_hstate.napping = 0;
 	vcpu->cpu = vc->pcpu;
 	smp_wmb();
-#ifdef CONFIG_PPC_ICP_NATIVE
+#if defined(CONFIG_PPC_ICP_NATIVE) && defined(CONFIG_SMP)
 	if (vcpu->arch.ptid) {
 		tpaca->cpu_start = 0x80;
 		wmb();