Merge "libdm: Add a helper function for creating placeholder devices." am:...

Merge "libdm: Add a helper function for creating placeholder devices." am: 3460b752 am: 1ab03512 am: 00a68cd5

Original change: https://android-review.googlesource.com/c/platform/system/core/+/2357843



Change-Id: If6d592affc75c41a1a4be29d2d1ae65c8474d570
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>