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>

arch/x86/kernel/amd_iommu_init.c

@@ -1273,6 +1273,11 @@ free:
 	goto out;
 }
 
+void amd_iommu_shutdown(void)
+{
+	disable_iommus();
+}
+
 /****************************************************************************
  *
  * Early detect code. This code runs at IOMMU detection time in the DMA