powerpc/powernv: Add support for powercap framework

powerpc/powernv: Add support for powercap framework

BugLink: http://bugs.launchpad.net/bugs/1718293
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>
(backported from commit cb8b340de21e1c57e1c6d4f26ccc4af46a3ed559)
Signed-off-by: Gustavo Walbon <gwalbon@linux.vnet.ibm.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>