PM / QoS: Use lockdep asserts to find missing hold of power.lock

Add lockdep asserts for holding the dev->power.lock to non-static
functions which require this. They could be used outside of the file so
asserts may help in detecting locking misuse.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>