drm/i915: Disable gpu reset on i965g/gm

Ville figured out that it needs a full display reset since apparently
a lot more goes down than just the GT. Until that's address it's
better to just diable gpu reset.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>