Merge "Downmix: Use internal ChannelMix if Downmix Effect unsupported" into sc-v2-dev am: c813bc53bb am: bd325815be

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/16105553

Change-Id: I1502aa9d5d94c2649e2c777c8bb1e23053fdbd12