x86: efi-payload64: Add bootstd support

Enable bootstd support for U-Boot at VirtualBox described at
https://source.denx.de/u-boot/u-boot/-/blob/master/doc/develop/bootstd.rst

This is used to boot system images at Virtualbox via
- distroboot (extlinux.conf)
- boot script

Signed-off-by: Thomas Mittelstaedt <thomas.mittelstaedt@bosch.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
[Added 'efi-payload64' tag]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
1 file changed