x86: Add initial video device init for Intel GMA

Intel's Graphics Media Accelerator (GMA) is a generic name for a wide range
of video devices. Add code to set up the hardware on ivybridge. Part of the
init happens in native code, part of it happens in a 16-bit option ROM for
those nostalgic for the 1970s.

Signed-off-by: Simon Glass <sjg@chromium.org>