iommu/amd: Document ivrs_ioapic and ivrs_hpet parameters

Document the new kernel commandline parameters in the
appropriate file.
Reviewed-by: NShuah Khan <shuahkhan@gmail.com>
Signed-off-by: NJoerg Roedel <joro@8bytes.org>

Documentation/kernel-parameters.txt

@@ -1226,6 +1226,20 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
 	iucv=		[HW,NET]
 
+	ivrs_ioapic	[HW,X86_64]
+			Provide an override to the IOAPIC-ID<->DEVICE-ID
+			mapping provided in the IVRS ACPI table. For
+			example, to map IOAPIC-ID decimal 10 to
+			PCI device 00:14.0 write the parameter as:
+				ivrs_ioapic[10]=00:14.0
+
+	ivrs_hpet	[HW,X86_64]
+			Provide an override to the HPET-ID<->DEVICE-ID
+			mapping provided in the IVRS ACPI table. For
+			example, to map HPET-ID decimal 0 to
+			PCI device 00:14.0 write the parameter as:
+				ivrs_hpet[0]=00:14.0
+
 	js=		[HW,JOY] Analog joystick
 			See Documentation/input/joystick.txt.