Fix GRUB handling of the E6400 keyboard

This introduces a patch to grub which disables the coreboot
specific handling, allowing PS/2 keyboards to be handled the
same as i386-pc.  However this alone breaks the keyboard in
Linux, requiring coreboot to perform PS/2 initialization.

I think GRUB may be restoring the original configuration of
the PS/2 controller once it exits, and if coreboot doesn't
initialize the controller then it's restored to the default
state which Linux doesn't seem to like. I think the emulated
keyboard interface provided by the EC on the E6400 behaves
in a non-standard way that is incompatible with the old
coreboot specific handling.