Add LICENSE to fix lint warning am: 9fcdebef07 am: e024d5cae0 am: 0b1f01964c

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

Change-Id: I49f34a084520cc2f95e4e2f0936a6297e11c286e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>