cpufreq / intel_pstate: Add kernel command line option disable intel_pstate.

When intel_pstate is configured into the kernel it will become the
preferred scaling driver for processors that it supports.  Allow the
user to override this by adding:
   intel_pstate=disable
on the kernel command line.

Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 363e348..b335c45 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1131,6 +1131,11 @@
 			0	disables intel_idle and fall back on acpi_idle.
 			1 to 6	specify maximum depth of C-state.
 
+	intel_pstate=  [X86]
+		       disable
+		         Do not enable intel_pstate as the default
+		         scaling driver for the supported processors
+
 	intremap=	[X86-64, Intel-IOMMU]
 			on	enable Interrupt Remapping (default)
 			off	disable Interrupt Remapping