Add LICENSE to fix lint warning am: 9fcdebef07 am: e024d5cae0

Original change: https://android-review.googlesource.com/c/platform/external/libmpeg2/+/2399171

Change-Id: Iefae29fff46fe8e8ac98ae63146060408ad446ee
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>