drm/i915: Balance context pinning on reset cleanup

We pin when we submit to execlist queue. Balance
the pinning when the submitted queue is cleaned on reset.

Cc: Dave Gordon <david.s.gordon@intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Thomas Daniel <thomas.daniel@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_lrc.c

@@ -1751,6 +1751,7 @@ void intel_lr_context_free(struct intel_context *ctx)
 				intel_unpin_ringbuffer_obj(ringbuf);
 				i915_gem_object_ggtt_unpin(ctx_obj);
 			}
+			WARN_ON(ctx->engine[ring->id].unpin_count);
 			intel_destroy_ringbuffer_obj(ringbuf);
 			kfree(ringbuf);
 			drm_gem_object_unreference(&ctx_obj->base);