eDP Init Failure on Broadwell

[CoolStar Organization]

On a Broadwell based chromebook with upstream coreboot & SeaBIOS, SeaBIOS
fails to initialize the built-in display.

If coreboot is configured to run the optionrom, keep the VESA framebuffer
and use VESA mode 4117 (1024x768@16), coreboot initializes the eDP properly.

However, if coreboot is configured not to run the VGA optionrom and SeaBIOS
is configured to run it, the eDP doesn't initialize properly. HDMI out
works fine, but eDP doesn't from SeaBIOS.

I would prefer not to use SeaVGABIOS, but would rather want SeaBIOS to run
the Intel VGA BIOS as SeaVGABIOS has issues with certain bootloaders and
operating systems (even GRUB has a corrupt display with SeaVGABIOS in my
testing).