Export headers using cc_library_headers am: 393ff671f0

Original change: https://android-review.googlesource.com/c/platform/external/arm-trusted-firmware/+/2604251

Change-Id: Ia4b8f449fe1912e999757c3f042fffe61562554f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>