Change in coreboot[master]: arch/x86/postcar: Add x86_64 support

[Patrick Rudolph (Code Review)]

Hello Aaron Durbin, Arthur Heymans, Patrick Rudolph, build bot (Jenkins), Patrick Georgi, Martin Roth,

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

https://review.coreboot.org/c/coreboot/+/30500

to look at the new patch set (#20).

Change subject: arch/x86/postcar: Add x86_64 support
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arch/x86/postcar: Add x86_64 support

* Add support for loading GDT on x86_64.
* Add x86_64 assembly code to do the same as the x86_32 code.
* Separate x86_32 and x86_64 code.

Tested on qemu x86_32 and x86_64 using additional MTRRs.
Needs test on real hardware.

Change-Id: I1c190627f5f0ed6f82738cb99423892382899d7b
Signed-off-by: Patrick Rudolph 
---
M Documentation/arch/x86/index.md
M src/arch/x86/Makefile.inc
M src/arch/x86/exit_car.S
M src/arch/x86/gdt_init.S
4 files changed, 59 insertions(+), 9 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/00/30500/20