PM: domains: Store the closest hrtimer event of the domain CPUs

The arch timer can not wake up the Qualcomm Technologies, Inc. (QTI)
SoCs when the deepest CPUidle modes results in the SoC also to enter
the low power mode.

RSC is part of CPU subsystem and APSS rsc device is attached to cluster
power domain. RSC has to setup next hrtimer wakeup in CONTROL_TCS which
can wakeup the SoC from deepest low power states. The CONTROL_TCS does
this by writing next wakeup in always on domain timer when the SoC is
entering the low power state.

Add dev_pm_genpd_get_next_hrtimer() to get the genpd wakeup time.

Signed-off-by: Maulik Shah <quic_mkshah@quicinc.com>