drop most of the crappy vm86 code and replace it with a rewritten

drop most of the crappy vm86 code and replace it with a rewritten
version that has all assembler in a .S file and all C code in a .c
file. Also, remove requirement to move around between GDTs.

This version includes the suggestions from Peter to clean up CR0 manipulation
and to guard critical code paths by cli/sti. Tested and working on my hardware.

Signed-off-by: Stefan Reinauer <stepan@coresystems.de>
Acked-by: Peter Stuge <peter@stuge.se>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@4323 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1