[coreboot] Multiboot support

[Robert Millan]

Hi,

I'm thinking that it'd be interesting for coreboot to have direct support for
Multiboot, so that Multiboot kernels can be used directly without GRUB/FILO as
middle man (somewhat like this thing you call "LAB").

When I brought this up on IRC, Patrick expressed concerns about size.  I suppose
the best would be to give users the option to provide either coreboot tables or
Multiboot, whatever is needed for their payload, instead of adding both things
unconditionally.

Nevertheless I don't expect the basic Multiboot support to be excessively big.

If this idea sounds fine, I could provide a patch for v3.