vboot: rename FAFT_KEY_OVERIDE and clarify its use

Rename GBB flag FAFT_KEY_OVERRIDE to RUNNING_FAFT.
Add a comment to clarify its use.

BUG=b:124141368, chromium:965914
TEST=make clean && make runtests
BRANCH=none

Change-Id: Ib90de7a0d22b39898fc84be8c16ff34ea1d3b504
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/1977902
Tested-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
2 files changed