amd-iommu: disable IOMMU hardware on shutdown

When the IOMMU stays enabled the BIOS may not be able to finish the
machine shutdown properly. So disable the hardware on shutdown.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index 745579b..328592f 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -290,6 +290,8 @@
 void pci_iommu_shutdown(void)
 {
 	gart_iommu_shutdown();
+
+	amd_iommu_shutdown();
 }
 /* Must execute after PCI subsystem */
 fs_initcall(pci_iommu_init);