PM: domains: inform PM domain of a device's next wakeup

Some devices may have a predictable interrupt pattern while executing
usecases. An example would be the VSYNC interrupt associated with
display devices. A 60 Hz display could cause a interrupt every 16 ms. If
the device were in a PM domain, the domain would need to be powered up
for device to resume and handle the interrupt.

Entering a domain idle state saves power, only if the residency of the
idle state is met. Without knowing the idle duration of the domain, the
governor would just choose the deepest idle state that matches the QoS
requirements. The domain might be powered off just as the device is
expecting to wake up. If devices could inform PM frameworks of their
next event, the parent PM domain's idle duration can be determined.

So let's add the dev_pm_genpd_set_next_wakeup() API for the device to
inform PM domains of the impending wakeup. This information will be the
domain governor to determine the best idle state given the wakeup.

Signed-off-by: Lina Iyer <ilina@codeaurora.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>