[automerger skipped] Add LICENSE file for libdrm am: 4a39b41b8b -s ours

am skip reason: Merged-In Ia5bd5a907c21478e265218516c547549d98ea196 with SHA-1 588355adb6 is already in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/libdrm/+/15069527

Change-Id: I2046e8102fe7ac418c05fdcc5f2a5e4ced9c9929