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 <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201111144322.1659970-1-dwmw2@infradead.org

drivers/iommu/amd/init.c

@@ -1601,9 +1601,11 @@ static int __init init_iommu_one(struct amd_iommu *iommu, struct ivhd_header *h)
 	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