drm/hisilicon: fix build error without fbdev emulation

drm/hisilicon: fix build error without fbdev emulation

We cannot reference priv->fbdev outside of the #ifdef:

drivers/net/virtio_net.c:1881:12: error: 'virtnet_restore_up' defined but not used [-Werror=unused-function]
 static int virtnet_restore_up(struct virtio_device *vdev)
drivers/net/virtio_net.c:1859:13: error: 'virtnet_freeze_down' defined but not used [-Werror=unused-function]
 static void virtnet_freeze_down(struct virtio_device *vdev)

As the #ifdef is a bit annoying here, this removes it entirely
and uses an IS_ENABLED() check in it place where needed.

Fixes: b4dd9f1ffaba ("drm/hisilicon: Remove custom FB helper deferred setup")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[danvet: One step further, also remove the IS_ENABLED checks, core
no-ops out the fb helper functions that the cma helpers use. Discussed
with Arnd on dri-devel.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20170725180555.3699056-1-arnd@arndb.de
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>