Add ReBAR support for Novacustom notebooks

[PerAstraAdDeum]

The problem you're addressing (if any)

There are a few ways by which you can make use of an external GPU on notebook, mainly Thunderbolt and OCuLink.

There is a variety of modern graphics cards that rely on ReBAR for maximum performance. Some GPUs, like Intels ARC Alchemist series, even need them for proper functioning.

Describe the solution you'd like

To my knowledge, coreboot has support for ReBAR. I therefore propose to enable it on Dasharos firmware for Novacustom notebooks, and adding an UEFI option to turn it on and off.

Where is the value to a user, and who might that user be?

Making use of an external GPU can boost the computing power of a notebook tremendously. This benefits a range of applications, mainly Games and graphic-intense design work. By enabling ReBAR, the proper functioning and/or maximum performance (not accounting for bandwidth limitations etc.) is guaranteed.

Describe alternatives you've considered

I can't think of any at the moment.

Additional context

No response

[mkopec]

Working on this as part of enablement of coreboot on discrete GPU models (RTX 40 series use an 8GB BAR): Dasharo/edk2#161