KVM: PPC: Book3S HV: Fix build error in book3s_hv.c

When CONFIG_KVM_XICS is enabled, CPU_UP_PREPARE and other macros for
CPU states in linux/cpu.h are needed by arch/powerpc/kvm/book3s_hv.c.
Otherwise, build error as below is seen:

   gwshan@gwshan:~/sandbox/l$ make arch/powerpc/kvm/book3s_hv.o
    :
   CC      arch/powerpc/kvm/book3s_hv.o
   arch/powerpc/kvm/book3s_hv.c: In function ‘kvmppc_cpu_notify’:
   arch/powerpc/kvm/book3s_hv.c:3072:7: error: ‘CPU_UP_PREPARE’ \
   undeclared (first use in this function)

This fixes the issue introduced by commit <6f3bb809> ("KVM: PPC:
Book3S HV: kvmppc_host_rm_ops - handle offlining CPUs").

Fixes: 6f3bb809
Cc: stable@vger.kernel.org # v4.6
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Reviewed-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kvm/book3s_hv.c

@@ -27,6 +27,7 @@
 #include <linux/export.h>
 #include <linux/fs.h>
 #include <linux/anon_inodes.h>
+#include <linux/cpu.h>
 #include <linux/cpumask.h>
 #include <linux/spinlock.h>
 #include <linux/page-flags.h>