ACPI: kernel-parameters.txt : Add intel_idle.max_cstate

Add missing intel_idle.max_cstate in kernel-parameters.txt

Signed-off-by Masanari Iida <standby24x7@gmail.com>
Signed-off-by: NLen Brown <len.brown@intel.com>

Documentation/kernel-parameters.txt

@@ -1035,6 +1035,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			By default, super page will be supported if Intel IOMMU
 			has the capability. With this option, super page will
 			not be supported.
+
+	intel_idle.max_cstate=	[KNL,HW,ACPI,X86]
+			0	disables intel_idle and fall back on acpi_idle.
+			1 to 6	specify maximum depth of C-state.
+
 	intremap=	[X86-64, Intel-IOMMU]
 			on	enable Interrupt Remapping (default)
 			off	disable Interrupt Remapping