SCPI protocol supports device power state management. This deals with
power states of various peripheral devices in the system other than the
core compute subsystem.

This patch adds support for the power state management of those
peripheral devices.
Tested-by: NMathieu Poirier <mathieu.poirier@linaro.org>
Tested-by: NJon Medhurst <tixy@linaro.org>
Reviewed-by: NJon Medhurst <tixy@linaro.org>
Reviewed-by: NKevin Hilman <khilman@baylibre.com>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Signed-off-by: NSudeep Holla <sudeep.holla@arm.com>