powerpc/powernv: Add support for powercap framework

Adds a generic powercap framework to change the system powercap
inband through OPAL-OCC command/response interface.

Signed-off-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Documentation/ABI/testing/sysfs-firmware-opal-powercap

@@ -0,0 +1,31 @@
+What:		/sys/firmware/opal/powercap
+Date:		August 2017
+Contact:	Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
+Description:	Powercap directory for Powernv (P8, P9) servers
+
+		Each folder in this directory contains a
+		power-cappable component.
+
+What:		/sys/firmware/opal/powercap/system-powercap
+		/sys/firmware/opal/powercap/system-powercap/powercap-min
+		/sys/firmware/opal/powercap/system-powercap/powercap-max
+		/sys/firmware/opal/powercap/system-powercap/powercap-current
+Date:		August 2017
+Contact:	Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
+Description:	System powercap directory and attributes applicable for
+		Powernv (P8, P9) servers
+
+		This directory provides powercap information. It
+		contains below sysfs attributes:
+
+		- powercap-min : This file provides the minimum
+		  possible powercap in Watt units
+
+		- powercap-max : This file provides the maximum
+		  possible powercap in Watt units
+
+		- powercap-current : This file provides the current
+		  powercap set on the system. Writing to this file
+		  creates a request for setting a new-powercap. The
+		  powercap requested must be between powercap-min
+		  and powercap-max.