[automerge] Refactor and reuse some read device file logic 2p: cb8474d7b6

Original change: https://googleplex-android-review.googlesource.com/c/platform/hardware/interfaces/+/16887730

Bug: 190757198
Change-Id: I95313a8d0558268886bbfe7f216cf4730f1ea945
Merged-In: I9b58043d5ed321aa71ff4f23031df251ae89c407