This patch adds experimental support for TBB to the HiKey960 board. To
build and test with TBB modify the uefi-tools project platforms.config

+ATF_BUILDFLAGS=TRUSTED_BOARD_BOOT=1 GENERATE_COT=1 SAVE_KEYS=1 \
  MBEDTLS_DIR=./mbedtls

Signed-off-by: Teddy Reed <teddy@casualhacking.io>