Looking at kconfig, the mainboard should select  MAINBOARD_HAS_LIBGFXINIT. 

For example see "grep -rsn MAINBOARD_HAS_LIBGFXINIT src/"

I haven't  used this, so not sure what else might be needed.

In order to get the build to progress I have needed to select MAINBOARD_HAS_LIBGFXINIT and MAINBOARD_USE_LIBGFXINIT.  The build now fails during compilation with:

    GCC        ramstage/libgfxinit/common/dyncpu/hw-gfx-gma-config.o
hw-gfx-gma-config.ads:19:32: missing operand
Makefile:356: recipe for target 'build/ramstage/libgfxinit/common/dyncpu/hw-gfx-gma-config.o’ failed

This feels like a rabbit hold down which I don’t want to find myself!

-Andy.