KVM: x86: fix build with !CONFIG_SMP

<asm/apic.h> isn't included directly and without CONFIG_SMP, an option
that automagically pulls it can't be enabled.
Reported-by: NJim Davis <jim.epost@gmail.com>
Signed-off-by: NRadim Krčmář <rkrcmar@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx.c

@@ -45,6 +45,7 @@
 #include <asm/perf_event.h>
 #include <asm/debugreg.h>
 #include <asm/kexec.h>
+#include <asm/apic.h>
 
 #include "trace.h"