payloads/external: Add more option related to SeaBIOS and GRUB2

Also known as "SeaGRUB", running GRUB2 atop SeaBIOS proves to be a
useful configuration, since SeaBIOS has improved its hardware
compatibility. For example, some USB drive can work under SeaBIOS but
do not work under native GRUB2, and GRUB2 can use BIOS call (provided
by SeaBIOS) as a fallback method to access hardware if it is present.

But more option is added addition to "SeaGRUB": now GRUB2 and SeaBIOS
can be built as secondary payloads, and "SeaGRUB" is now implemented
as "Primary SeaBIOS + Secondary GRUB2 (selected) + config files".

Signed-off-by: Bill XIE <persmule@hardenedlinux.org>
Change-Id: Ie681fa231abfe4a8f1e4510b3c17957550a9d2f8
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60640
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@tutanota.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

0 files changed, 0 insertions, 0 deletions