lib: trusty: add `handle_ref_is_attached` to use from rust am: 3ab7c616ac

Original change: https://android-review.googlesource.com/c/trusty/lk/trusty/+/3434479

Change-Id: Ia9cd324b729218bf37ac9ad5f8f70212db3ae8c5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>