iommu/vt-d: include conditionally on CONFIG_INTEL_IOMMU_SVM

Commit 6ee1b77b ("iommu/vt-d: Add svm/sva invalidate function")
introduced intel_iommu_sva_invalidate() when CONFIG_INTEL_IOMMU_SVM.
This function uses the dedicated static variable inv_type_granu_table
and functions to_vtd_granularity() and to_vtd_size().

These parts are unused when !CONFIG_INTEL_IOMMU_SVM, and hence,
make CC=clang W=1 warns with an -Wunused-function warning.

Include these parts conditionally on CONFIG_INTEL_IOMMU_SVM.

Fixes: 6ee1b77b

 ("iommu/vt-d: Add svm/sva invalidate function")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20201115205951.20698-1-lukas.bulwahn@gmail.com
Signed-off-by: Will Deacon <will@kernel.org>