drm/i915: rip out gen2 reset code

At least on my i830M here it reliably results in hard system hangs
nowadays. This is much worse than falling back to software rendering,
so I think we should simply rip this out.

After all we don't have any gpu reset for gen3 either, and there are a
lot more of those still around.

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