Change in coreboot[master]: cbfstool/linux_trampoline: Fill the ACPI RSDP entry

[Arthur Heymans (Code Review)]

Attention is currently required from: Arthur Heymans, ron minnich.
Hello build bot (Jenkins), Nico Huber, Angel Pons, Arthur Heymans, ron minnich,

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

https://review.coreboot.org/c/coreboot/+/62574

to look at the new patch set (#7).

Change subject: cbfstool/linux_trampoline: Fill the ACPI RSDP entry
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cbfstool/linux_trampoline: Fill the ACPI RSDP entry

With LinuxBoot Linux relied on the legacy method of fetching the RSDP
pointer to get ACPI. This uses a more modern approach available since
2018 on the Linux kernel, which involves filling in the zero page.

This method takes precedence over any other method of fetching the
RSDP in Linux (UEFI, Kexec, Legacy/BIOS). Some UEFI zealots are
threatening that legacy code will be removed from Linux so it's best
to already adapt to that possibility.

Tested on Qemu:
- With qemu the RSDP is always in the EBDA, so checking if Linux uses
  the provided pointer is better done with a forced bad entry
- With a fake bad pointer Linux correctly does not find RDSP

Change-Id: I688b94608b03b0177c42d2834c7e3beb802ae686
Signed-off-by: Arthur Heymans 
---
M util/cbfstool/linux_trampoline.S
M util/cbfstool/linux_trampoline.c
2 files changed, 22 insertions(+), 9 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/74/62574/7