kvm tools: Define KVM_VIRTIO_MMIO_AREA for powerpc

Commit 82ea06e "Introduce KVM_VIRTIO_MMIO_AREA" did just that, but only
for x86. Causing the following commit 5c301a3 "Add virtio-mmio support"
to break the build for powerpc.

We follow what x86 did and place it 16MB past the PCI area, I have no
idea if that is actually a good idea, or whether it works at all.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

powerpc/include/kvm/kvm-arch.h

@@ -39,6 +39,7 @@
  * from.  Note that this is a PCI bus address.
  */
 #define KVM_PCI_MMIO_AREA		0x1000000
+#define KVM_VIRTIO_MMIO_AREA		0x2000000
 
 struct spapr_phb;