[coreboot] suspend/resume in v3

[Rudolf Marek]

> CAR will write to memory locations below 1M. There are three ways to
> cope with that:
> 1. Back up that area during suspend and restore it as last instruction
> of resume.
> 2. Declare the CAR area (48 kB) as reserved memory.

Imho this is OK, and easiest.

> 3. Write excessively clever and fragile code which performs a double
> stack switch during resume.


Here are some other ideas, might not work if stack is never realocated. I dont 
know how CAR in v3 works.

4. use 0xA0000-0xBFFFF

I think we can use this RAM because it will be covered by SMM (done by us) or 
will be covered by legacy VGA anyway.

5.  use 0xf0000-0xfffff

It will get overwritten by some our code, before that we might use it.

Rudolf