AMD IOMMU: enable device isolation per default

Impact: makes device isolation the default for AMD IOMMU

Some device drivers showed double-free bugs of DMA memory while testing
them with AMD IOMMU. If all devices share the same protection domain
this can lead to data corruption and data loss. Prevent this by putting
each device into its own protection domain per default.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index b56ee02..f2e1e7f 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -294,7 +294,7 @@
 			Possible values are:
 			isolate - enable device isolation (each device, as far
 			          as possible, will get its own protection
-			          domain)
+			          domain) [default]
 			share - put every device behind one IOMMU into the
 				same protection domain
 			fullflush - enable flushing of IO/TLB entries when