drm/i915: Only mark as map-and-fenceable when bound into the GGTT

We use the obj->map_and_fenceable hint for when we already have a
valid mapping of this object in the aperture. This hint can only apply
to the GGTT and not to the aliasing-ppGTT. One user of the hint is
execbuffer relocation, which began to fail when it tried to follow the
hint and perform the relocate through the non-existent GGTT mapping.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=85671


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