iommu/vt-d: Don't dereference iommu_device if IOMMU_API is not built

Since commit c40aaaac10 ("iommu/vt-d: Gracefully handle DMAR units
with no supported address widths") dmar.c needs struct iommu_device to
be selected. We can drop this dependency by not dereferencing struct
iommu_device if IOMMU_API is not selected and by reusing the information
stored in iommu->drhd->ignored instead.

This fixes the following build error when IOMMU_API is not selected:

drivers/iommu/intel/dmar.c: In function ‘free_iommu’:
drivers/iommu/intel/dmar.c:1139:41: error: ‘struct iommu_device’ has no member named ‘ops’
 1139 |  if (intel_iommu_enabled && iommu->iommu.ops) {
                                                ^

Fixes: c40aaaac10 ("iommu/vt-d: Gracefully handle DMAR units with no supported address widths")
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20201013073055.11262-1-brgl@bgdev.pl
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel/dmar.c

@@ -1133,7 +1133,7 @@ error:
 
 static void free_iommu(struct intel_iommu *iommu)
 {
-	if (intel_iommu_enabled && iommu->iommu.ops) {
+	if (intel_iommu_enabled && !iommu->drhd->ignored) {
 		iommu_device_unregister(&iommu->iommu);
 		iommu_device_sysfs_remove(&iommu->iommu);
 	}