Change in coreboot[master]: payloads/external/LinuxBoot: Adopt u-root change

[Patrik Tesarik (Code Review)]

Hello build bot (Jenkins), Patrick Georgi, Martin Roth, Christian Walter,  Marcello Sylvester Bauer,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/40316

to look at the new patch set (#10).

Change subject: payloads/external/LinuxBoot: Adopt u-root change
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payloads/external/LinuxBoot: Adopt u-root change

The u-root toolkit dropped the original uinit bootloader in the master
branch and respectively the systemboot-option in templates.go. In consequence
the LinuxBoot builds will boot into the u-root shell and waiting for input.
This commit enables the reuse of the -uinitcmd flag to specify a command, which
runs after the u-root init-process.

Systemboot as a bootloader wrapper will mimick a BIOS/UEFI boot device
selection. Other preselections, i.e. stboot and boot2 are implemented as well.
Custom strings or programs can be set as well, but they cannot contain program
flags. E.g. 'fbnetboot -class linuxboot' will not work, because they aren't
symlinkable.

This commit and its respective LinuxBoot builds with systemboot, none
and one custom option have been tested successfully on a UP squared
single board computer with the intended behavior.

Change-Id: I4ac3409040ea77a1836f90f43fba07d2cd05a952
Signed-off-by: Patrik Tesarik 
---
M payloads/external/LinuxBoot/Kconfig
M payloads/external/LinuxBoot/targets/u-root.mk
M payloads/external/Makefile.inc
3 files changed, 59 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/16/40316/10