Geminilake devices use the FSP PEI GOP driver for display init, so the display backlight will come on during ramstage (when FSP-S runs), but the platform does not currently support any output / proof of life prior to the payload, other than maybe an early boot splash screen (you'd have to look if GLK supports that).
The truth is though, if your device doesn't boot to the OS, you're going to need to debug it, and having an indication that it failed in coreboot vs the payload isn't all that useful when simply connecting the debug cable and flashing a serial output enabled build will tell you the same thing