pm: device: Get rid of z_pm_core_devices

z_pm_core_devices was hack to set some priority between devices. It
was doing it hardcoding some devices that were the first to bring up
and the last to power down. Remove it and use the same list used to
initialize devices.

Fixes #34214

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>