PM: domains: Store the next hrtimer wakeup in genpd

The arch timer cannot wake up the Qualcomm Technologies, Inc. (QTI) SoCs
from the deeper CPUidle states. To be able to wakeup from these deeper
states, another always-on timer needs to be programmed through the so
called CONTROL_TCS.

As the RSC is part of CPU subsystem and the corresponding APSS RSC device
is attached to the cluster PM domain (through genpd), it holds the
responsibility to program the always-on timer, before entering any of these
deeper CPUidle states.

However, programming the timer requires information about the next hrtimer
wakeup for the cluster PM domain, which is currently only known by genpd.
Therefore, let's share this data through a new genpd helper function,
dev_pm_genpd_get_next_hrtimer().

Signed-off-by: Maulik Shah <quic_mkshah@quicinc.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
[Ulf: Reworked the code and updated the commit message]
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> # SM8450
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221018152837.619426-5-ulf.hansson@linaro.org