of/platform: Implement support for dev_pm_ops

Linux power management subsystem supports vast amount of new PM
callbacks that are crucial for proper suspend and hibernation support
in drivers.

This patch implements support for dev_pm_ops, preserving support
for legacy callbacks.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>