[coreboot] stack sizes in v2

[Carl-Daniel Hailfinger]

Hi,

Stefan pointed out that we only have 8 kB stack on most v2 boards.
AFAICS that limitation is only present in RAM code, whereas CAR code has
at least 16 kB. That's backwards and I didn't find any reason for it.
LZMA code uses ~16 kB stack for decompression, so if the LZMA
decompression runs with a small stack, we smash everything in that area.

Two questions:
- Do we really only have 8 kB stack?
- Any reason not to increase this to 64 kB or so since RAM is plentiful?

Regards,
Carl-Daniel