Allow drivers, that belong to subsystems which use the generic
runtime pm callbacks, not to define runtime pm suspend/resume handlers,
by implicitly assuming success in such cases.

This is needed to eliminate nop handlers that would otherwise be
necessary by drivers which enable runtime pm, but don't need
to do anything when their devices are runtime-suspended/resumed.
Signed-off-by: NOhad Ben-Cohen <ohad@wizery.com>
Acked-by: NKevin Hilman <khilman@deeprootsystems.com>
Acked-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

There are subsystems whose power management callbacks only need to
invoke the callbacks provided by device drivers.  Still, their system
sleep PM callbacks should play well with the runtime PM callbacks,
so that devices suspended at run time can be left in that state for
a system sleep transition.

Provide a set of generic PM callbacks for such subsystems and
define convenience macros for populating dev_pm_ops structures.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>