drm/i915: Don't WARN about ring idle bit on gen2

Gen2 doesn't have the ring idle/stop bits in the SCPD/MI_MODE register,
so don't go spewing warnings about the state of those bits.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1494,7 +1494,7 @@ void intel_cleanup_ring_buffer(struct intel_engine_cs *ring)
 		return;
 
 	intel_stop_ring_buffer(ring);
-	WARN_ON((I915_READ_MODE(ring) & MODE_IDLE) == 0);
+	WARN_ON(!IS_GEN2(ring->dev) && (I915_READ_MODE(ring) & MODE_IDLE) == 0);
 
 	iounmap(ringbuf->virtual_start);