[coreboot] Are multiple GPUs with lots of memory (ex: 8GB+8GB) supported in coreboot?

[Taiidan at gmx.com]

I would like to add this information to the wiki so I am wondering if 
anyone has successfully used for instance dual 8GB graphics cards with 
coreboot.

I am not sure if this would be an issue due to coreboot only having 
32bit MMIO space.

Thanks!