[automerger skipped] Prepare for having audio_channel_mask_t as an enum type am: 2b3cc98138 -s ours

am skip reason: Change-Id I42506484b1d0b0482618b7314fad4c8012a06fb4 with SHA-1 55773033ed is in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/12787292

Change-Id: I7b014d685dbd091ed61d2300294a50f50c191877