Merge "Allow to register RENDER AudioMix pointing to previously registered LOOPBACK AudioMix." into udc-dev am: 55825ec1d0 am: beac804347

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/23693534

Change-Id: Iff297a9a1517fc933c02dec1824652d61e5257d9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>