ARM: zynq: Add cpuidle support

Add cpuidle support for Xilinx Zynq.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Merge branch 'pm-cpuidle-next' into bleeding-edge

* pm-cpuidle-next:
  ARM: zynq: Add cpuidle support