KVM: PPC: do not compile in vfio.o unconditionally

Build on 32-bit PPC fails with the following error:

 int kvm_vfio_ops_init(void)
      ^
 In file included from arch/powerpc/kvm/../../../virt/kvm/vfio.c:21:0:
 arch/powerpc/kvm/../../../virt/kvm/vfio.h:8:90: note: previous definition of ‘kvm_vfio_ops_init’ was here
 arch/powerpc/kvm/../../../virt/kvm/vfio.c:292:6: error: redefinition of ‘kvm_vfio_ops_exit’
 void kvm_vfio_ops_exit(void)
             ^
 In file included from arch/powerpc/kvm/../../../virt/kvm/vfio.c:21:0:
 arch/powerpc/kvm/../../../virt/kvm/vfio.h:12:91: note: previous definition of ‘kvm_vfio_ops_exit’ was here
 scripts/Makefile.build:258: recipe for target arch/powerpc/kvm/../../../virt/kvm/vfio.o failed
 make[3]: *** [arch/powerpc/kvm/../../../virt/kvm/vfio.o] Error 1

Check whether CONFIG_KVM_VFIO is set before including vfio.o
in the build.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/powerpc/kvm/Makefile

diff --git a/arch/powerpc/kvm/Makefile b/arch/powerpc/kvm/Makefile
index 7f7b6d8..eba0bea 100644
--- a/arch/powerpc/kvm/Makefile
+++ b/arch/powerpc/kvm/Makefile
@@ -8,7 +8,8 @@
 KVM := ../../../virt/kvm
 
 common-objs-y = $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o \
-		$(KVM)/eventfd.o $(KVM)/vfio.o
+		$(KVM)/eventfd.o
+common-objs-$(CONFIG_KVM_VFIO) += $(KVM)/vfio.o
 
 CFLAGS_e500_mmu.o := -I.
 CFLAGS_e500_mmu_host.o := -I.