firmware/2lib: Handle errors in alternate boot

Handle three different errors in alternate boot:
- VB2_UI_ERROR_ALTERNATE_BOOT_DISABLED
- VB2_UI_ERROR_NO_BOOTLOADER
- VB2_UI_ERROR_ALTERNATE_BOOT_FAILED

BUG=b:146399181, b:161092974
TEST=make clean && make runtests
BRANCH=puff, zork

Cq-Depend: chromium:2384995
Signed-off-by: Hsuan Ting Chen <roccochen@chromium.org>
Change-Id: I1e6572ed4a1c756d6d3727818439de25cad03158
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2382998
Tested-by: Shelley Chen <shchen@chromium.org>
Reviewed-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-by: Shelley Chen <shchen@chromium.org>
2 files changed