Revert "Revert "coreboot/e6400nvidia: don't run vga rom""

This reverts commit 4ee5e2af.

I thought maybe coreboot init would work better, but i get the same
problem: xorg doesn't start at all, when using the nouveau driver.

However, booting to tty works fine, and you can run xorg with
the nomodeset option (in Linux) at startup.