bootstd: Always create the EFI bootmgr bootmeth

Now that we can separate this out from the normal bootmeths, update the
code to create it always.

We cannot rely on the device tree to create this, since the EFI project
is quite opposed to having anything in the device tree that helps U-Boot
with its processing.

Signed-off-by: Simon Glass <sjg@chromium.org>