KVM: PPC: Book3S HV: use xics_wake_cpu only when defined

commit 48eaef0518a565d3852e301c860e1af6a6db5a84 upstream.

Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>