[emac] Release BIBs from emac board so they can be consumed by RTC and gpu repo

Change-Id: I26620249e0de0dfb0eeb043beff963817e0bf3fe
Reviewed-on: https://fuchsia-review.googlesource.com/c/boards/emac/+/1095312
Reviewed-by: Chase Latta <chaselatta@google.com>
Commit-Queue: Jiaming Li <lijiaming@google.com>
Reviewed-by: Darren Chan <chandarren@google.com>