Merge "Downmix : Add libeffect implementation" am: f1a9007f3d am: ecc90a6127 am: ba1af68dcd

Original change: https://android-review.googlesource.com/c/platform/frameworks/av/+/2353846

Change-Id: If3e48fae8232a0db9ef1d5d41ada85004f889ea7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>