C2: add support for channel mask am: 65fab753

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/17478658



Change-Id: I9f3be5f23cb0703b741bd007b266c9386008c569
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>