Change in coreboot[master]: arch/x86/postcar: Use a separate stack for C execution

[Arthur Heymans (Code Review)]

Attention is currently required from: Raul Rangel, Lee Leahy, Huang Jin, Kyösti Mälkki, Patrick Rudolph, Aaron Durbin.
Arthur Heymans has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/54298 )

Change subject: arch/x86/postcar: Use a separate stack for C execution
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Patch Set 6:

(1 comment)

File src/arch/x86/exit_car.S:

https://review.coreboot.org/c/coreboot/+/54298/comment/d2cba8b4_0b715984 
PS6, Line 108: mov	post_car_stack_top, %esp
> Can we use `_estack`  now?

Not yet (done at line 189). It's still weirdly called post_car_stack_top here but that's only because that's how the MTRR setup is passed to postcar so it's just a bad name now. I the next CL this is dropped so I didn't bother renaming it.