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!