Merge "Create libstagefright_mp3dec_headers" am: e9ebb9efbc am: e54bbcdfea am: 89715382dc

Original change: https://android-review.googlesource.com/c/platform/frameworks/av/+/1525002

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: If9d8b5e9e1648d85c728dcb50bb0a7e2f01a29f2