drm/i915: Set up a render context on Ironlake

RC6 power state requires a logical render context in place for saving
render context.

Signed-off-by: Zou Nan hai <nanhai.zou@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_drv.h

@@ -254,6 +254,7 @@ typedef struct drm_i915_private {
 	drm_local_map_t hws_map;
 	struct drm_gem_object *seqno_obj;
 	struct drm_gem_object *pwrctx;
+	struct drm_gem_object *renderctx;
 
 	struct resource mch_res;