Merge "Add KM_PURPOSE_AGREE_KEY constant." am: 203813672e am: 4f136a5659 am: 1fa7495b89

Original change: https://android-review.googlesource.com/c/platform/hardware/libhardware/+/1556301

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I5d8a778dd90b93a2b74c13f475c1b34f241e76c2