ARM: imx6: pm: declare pm domain latency on power_state struct

The generic_pm_domain structure uses an array of latencies to be able to
declare multiple intermediate states.

Declare a single "OFF" state with the default latencies So that the
power_off_latency_ns and power_on_latency_ns fields of generic_pm_domain
structure can be eventually removed.

[ Lina: pm_genpd_init() argument changev ]
Signed-off-by: Lina Iyer <lina.iyer@linaro.org>
Signed-off-by: Axel Haslam <ahaslam+renesas@baylibre.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>