Add LICENSE to fix lint warning am: 9fcdebef07

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

Change-Id: Ic93db3cd4007288d197575bfc4afca9d12abfb46
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>