[x200] No DisplayPort output in GRUB

While DisplayPort works fine in GNU/Linux, the external monitor remains black in GRUB.
It would be nice if GRUB would also output to an external DP monitor when docked.

This probably shares code with issue #13.

[ArthurHeymans]

I think the best idea to add DP and DVI/HDMI/SDVO is to port the G(M)45 GMCH graphic init to libgfxinit (ada/spark). The C code to do this is ugly and requires a major refactoring.