init.qcom.rc: Add a custom shutdown trigger to kill rmtfs am: 66a926c714 am: d3b26ba98f am: 33d78833de

Original change: https://android-review.googlesource.com/c/device/linaro/dragonboard/+/1331554

Change-Id: I61ebea5d79cef43111e6653a275bb7f945e55b2c