PPC: KVM: Compile fix for qemu_notify_event

PPC: KVM: Compile fix for qemu_notify_event

The function qemu_notify_event is defined by a header that we don't
include in the PPC KVM code. Include it to get the code building
again.

  target-ppc/kvm_ppc.c: In function 'kvmppc_timer_hack':
  target-ppc/kvm_ppc.c:26:5: error: implicit declaration of function 'qemu_notify_event' [-Werror=implicit-function-declaration]
  target-ppc/kvm_ppc.c:26:5: error: nested extern declaration of 'qemu_notify_event' [-Werror=nested-externs]

Signed-off-by: Alexander Graf <agraf@suse.de>