intel_pstate: provide option to only use intel_pstate with HWP

Allow users the option to disable the driver for any hardware
which does not support HWP.

Signed-off-by: Kristen Carlson Accardi <kristen@linux.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 4df73da..07e6701 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1469,6 +1469,9 @@
 		       no_hwp
 		         Do not enable hardware P state control (HWP)
 			 if available.
+		hwp_only
+			Only load intel_pstate on systems which support
+			hardware P state control (HWP) if available.
 
 	intremap=	[X86-64, Intel-IOMMU]
 			on	enable Interrupt Remapping (default)