drm/i915: Ensure that if we ever try to pin+fence it is mappable.

When merging Daniel's full-gtt patches I had a set of tweaks which I
thought I had undone. I was half right...

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=31286
Reported-by: jinjin.wang@intel.com
Reported-by: Alexey Fisher <bug-track@fisher-privat.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_gem.c

@@ -4151,6 +4151,7 @@ i915_gem_object_pin(struct drm_gem_object *obj, uint32_t alignment,
 	int ret;
 
 	BUG_ON(obj_priv->pin_count == DRM_I915_GEM_OBJECT_MAX_PIN_COUNT);
+	BUG_ON(need_fence && !mappable);
 	WARN_ON(i915_verify_lists(dev));
 
 	if (obj_priv->gtt_space != NULL) {

drivers/gpu/drm/i915/intel_display.c

@@ -1462,7 +1462,8 @@ intel_pin_and_fence_fb_obj(struct drm_device *dev,
 	}
 
 	ret = i915_gem_object_pin(obj, alignment,
-				  !pipelined, obj_priv->tiling_mode);
+				  !pipelined || obj_priv->tiling_mode,
+				  obj_priv->tiling_mode);
 	if (ret)
 		return ret;