vboot: standardize legacy boot and altfw terminology

Standardize on the term "altfw" (short form) and
"alternate bootloader" (long form) in both code and

Remove the VbAltFwIndex_t enum, and replace with a
simple uint32_t.

Rename VbExLegacy to vb2ex_run_altfw, and move
to vboot2 namespace.

Rename crossystem param dev_boot_legacy to
dev_boot_altfw, but leave an alias.

Rename crossystem param dev_default_boot value
from legacy to altfw, but leave an alias.

TEST=make clean && make runtests
TEST=emerge vboot_reference and check output for:
     crossystem dev_boot_legacy=0
     crossystem dev_boot_altfw=0
     crossystem dev_default_boot=legacy
     crossystem dev_default_boot=altfw

Cq-Depend: chromium:2641196
Signed-off-by: Joel Kitching <kitching@google.com>
Change-Id: I289df63d992a3d9ae3845c59779ecbd115b18ee2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2641346
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@chromium.org>
Tested-by: Joel Kitching <kitching@chromium.org>
Commit-Queue: Yu-Ping Wu <yupingso@chromium.org>
22 files changed