iommu/vt-d: Add a command line parameter for VT-d posted-interrupts

Enable VT-d Posted-Interrtups and add a command line
parameter for it.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Joerg Roedel <joro@8bytes.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 22a4b68..73588fc 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1553,6 +1553,7 @@
 			nosid	disable Source ID checking
 			no_x2apic_optout
 				BIOS x2APIC opt-out request will be ignored
+			nopost	disable Interrupt Posting
 
 	iomem=		Disable strict checking of access to MMIO memory
 		strict	regions from userspace.