iommu/vt-d: Request passthrough mode from IOMMU core

Get rid of the iommu_pass_through variable and request
passthrough mode via the new iommu core function.
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel-iommu.c

@@ -3267,7 +3267,7 @@ static int __init init_dmars(void)
 		iommu->flush.flush_iotlb(iommu, 0, 0, 0, DMA_TLB_GLOBAL_FLUSH);
 	}
 
-	if (iommu_pass_through)
+	if (iommu_default_passthrough())
 		iommu_identity_mapping |= IDENTMAP_ALL;
 
 #ifdef CONFIG_INTEL_IOMMU_BROKEN_GFX_WA