hikey960: Add /metadata support (reusing cache partition) am: e8fe717c88 am: b754c17dea am: e97fb06202

Original change: https://android-review.googlesource.com/c/device/linaro/hikey/+/1584533

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ib6579ebc9eba849f352e98a291699e04ed3e8548