thermal: core: Relocate thermal zone initialization routine

Move thermal_zone_device_init() along with thermal_zone_device_check()
closer to the callers of the former, where they fit better together.

No functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/1906685.CQOukoFCf9@rjwysocki.net