vboot/ui: add developer and to_norm screens

Developer mode can boot internal or external disk.  Support for
booting legacy firmware ("Ctrl+L") will be added in a subsequent CL.

TEST=make clean && make runtests

Change-Id: I45590e20727bd84375d10ca5ef906206d0ecd805
Signed-off-by: Joel Kitching <kitching@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2192863
Tested-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
7 files changed