[M] Change in coreboot[main]: arch/x86: Enable long mode entry into payload for x86_64 support

[Patrick Rudolph (Code Review)]

Attention is currently required from: Arthur Heymans, Julius Werner, Jérémy Compostella, Kapil Porwal, Nico Huber, Subrata Banik.

Patrick Rudolph has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/81960?usp=email )

Change subject: arch/x86: Enable long mode entry into payload for x86_64 support
......................................................................

Patch Set 7:

(1 comment)

File src/arch/x86/boot.c:

https://review.coreboot.org/c/coreboot/+/81960/comment/84ff50e0_3d6bcb67 :
PS3, Line 47: is_payload_64_bit_enabled
> > > I'd assume a call to die() or assembly code to set up long mode before jumping to payload. […]

On x86_32 coreboot you do not properly handle the case when someone inserts a 64-bit payload into the CBFS. Since the flag is a build time option and you only evaluate it at runtime at end of boot, there should be either support for it or an error message.