vboot: use VB2_SD_FLAG_KERNEL_SIGNED

Use vboot2 variant VB2_SD_FLAG_KERNEL_SIGNED instead of
vboot1 VBSD flag VBSD_KERNEL_KEY_VERIFIED.  Export the
flag back to vboot1 at the end of VBSLK.

BUG=b:124141368, chromium:1038260
TEST=make clean && make runtests
BRANCH=none

Change-Id: Ie7516195b95a9ef2ca254616c9486991b1a418fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2053181
Tested-by: Joel Kitching <kitching@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
Reviewed-by: Joel Kitching <kitching@chromium.org>
3 files changed