Revert "drm/i915: reenable gmbus on gen3+ again"

This reverts commit c3dfefa0.

gmbus in 3.4 has simply too many known issues:
- gmbus is too noisy, we need to rework the logging:
  https://bugs.freedesktop.org/show_bug.cgi?id=48248
- zero-length writes cause an OOPS, and they are
  userspace-triggerable:
  https://lkml.org/lkml/2012/3/30/176
- same for zero-length reads:
  https://bugs.freedesktop.org/show_bug.cgi?id=48269

We can try again for 3.5.
Acked-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_i2c.c

@@ -390,7 +390,7 @@ int intel_setup_gmbus(struct drm_device *dev)
 		bus->has_gpio = intel_gpio_setup(bus, i);
 
 		/* XXX force bit banging until GMBUS is fully debugged */
-		if (bus->has_gpio && IS_GEN2(dev))
+		if (bus->has_gpio)
 			bus->force_bit = true;
 	}