powerpc/85xx: Add power management support for MPC85xxMDS boards

- Add power management controller nodes;
- Add interrupts for RTC nodes, the RTC interrupt may be used as a
  wakeup source;
- Add sleep properties (DEVDISR bit mask) and sleep-nexus nodes.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>