Add support for handling this concept in bootflows. Update the 'bootflow'
command to allow only the normal bootmeths to be used. This alllows
skipping EFI bootmgr and VBE, for example.
Signed-off-by: Simon Glass <sjg@chromium.org>
With global bootmeths we want to scan without a bootdev. Update the logic
to allow this.
Change the bootflow command to show the bootdev only when valid.
Signed-off-by: Simon Glass <sjg@chromium.org>