iommu/vt-d: Expose struct svm_dev_ops without CONFIG_INTEL_IOMMU_SVM

The point in providing an inline version of intel_svm_bind_mm() which
just returns -ENOSYS is that people are supposed to be able to *use* it
and just see that it fails. So we need to let them have a definition of
struct svm_dev_ops (and the flags) too.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>