agp/intel: split out gmch/gtt probe, part 2

This just splits the device list into two and moves the gtt related stuff
to intel-gtt.c. The two new devices lists also lose the not longer needed
fields. There where only about 5 cases anyway with both a gmch and a
possible agp port, so the duplication of entries is rather small.
Additionally kill 2 out of the three Ironlake mobile entries that
only differed in host bridge pci id.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>