Documentation: Update Documentation for iommu.passthrough

This kernel parameter now takes also effect on X86.
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Documentation/admin-guide/kernel-parameters.txt

@@ -1811,7 +1811,7 @@
 			  synchronously.
 
 	iommu.passthrough=
-			[ARM64] Configure DMA to bypass the IOMMU by default.
+			[ARM64, X86] Configure DMA to bypass the IOMMU by default.
 			Format: { "0" | "1" }
 			0 - Use IOMMU translation for DMA.
 			1 - Bypass the IOMMU for DMA.