init: Fire shutdown trigger for thermal shutdown

Recent change in init has bring normal shutdown sequence in
thermal-shutdown condition. This CL will make sure init fire shutdown
trigger where holds custom shutdown actions for vendor SoC/platform.

Bug: 63686426
Test: adb shell setprop sys.powerctl thermal-shutdown
Change-Id: Ieb8579fdf9c30c1a81d60466a7375c9784f3ca98