MLK-17074-8 soc: imx8: pm-domains: fix the wrong use of runtime_idle_active for pd...

MLK-17074-8 soc: imx8: pm-domains: fix the wrong use of runtime_idle_active for pd mode selection

There're fundanmental difference between the using of start/stop and pd
mode selection. Start/stop actually can only reflect device state, not
power domain state. So actually we're abusing it here.
e.g. take a consider of two devices on the same domain.

PD mode should be selected by power domain gorvernor or power domain core.
This patch totally remove the wrong use of start/stop and runtime_idle_active
to indicate which PD mode to enter.

By apply this patch, the power domain lower power mode selection will have
no dependency on the per device runtime status anymore.

Reviewed-by: Frank Li <frank.li@nxp.com>
Reviewed-by: Ranjani Vaidyanathan <Ranjani.Vaidyanathan@nxp.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>