spapr: Only report host/guest IOMMU page size mismatches on KVM

We print a warning if the spapr IOMMU isn't configured to support a page
size matching the host page size backing RAM.  When that's the case we need
more complex logic to translate VFIO mappings, which is slower.

But, it's not so slow that it would be at all noticeable against the
general slowness of TCG.  So, only warn when using KVM.  This removes some
noisy and unhelpful warnings from make check on hosts with page sizes
which typically differ from those on POWER (e.g. Sparc).
Reported-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>
Reviewed-by: NThomas Huth <thuth@redhat.com>

hw/ppc/spapr_pci.c

@@ -1745,7 +1745,8 @@ static void spapr_phb_realize(DeviceState *dev, Error **errp)
     }
 
     /* DMA setup */
-    if ((sphb->page_size_mask & qemu_getrampagesize()) == 0) {
+    if (((sphb->page_size_mask & qemu_getrampagesize()) == 0)
+        && kvm_enabled()) {
         error_report("System page size 0x%lx is not enabled in page_size_mask "
                      "(0x%"PRIx64"). Performance may be slow",
                      qemu_getrampagesize(), sphb->page_size_mask);