greybus: bundle: add runtime pm support

This patch adds runtime pm support for the bundle core. Unbound bundle
devices are always deactivated. During probe, Runtime PM status is set
to enabled and active and the usage count is incremented. If the driver
supports runtime PM, it should call pm_runtime_put() in its probe
routine and pm_runtime_get_sync() in remove routine as bundle needs to
be resume before it can be deactivated.

Testing Done:
 - Check runtime_status of the bundle driver when bundle goes to suspend

Signed-off-by: David Lin <dtwlin@google.com>
Signed-off-by: Axel Haslam <ahaslam@baylibre.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Alex Elder <elder@linaro.org>