iommu/amd: Don't register interrupt remapping irqdomain when IR is disabled

Registering the remapping irq domain unconditionally is potentially
allowing I/O-APIC and MSI interrupts to be parented in the IOMMU IR domain
even when IR is disabled. Don't do that.

Signed-off-by: David Woodhouse <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/iommu/amd/init.c

···
 	if (ret)
 		return ret;
 
-	ret = amd_iommu_create_irq_domain(iommu);
-	if (ret)
-		return ret;
+	if (amd_iommu_irq_remap) {
+		ret = amd_iommu_create_irq_domain(iommu);
+		if (ret)
+			return ret;
+	}
 
 	/*
 	 * Make sure IOMMU is not considered to translate itself. The IVRS