Make drm_encoder_helper_funcs and it's functions optional to avoid
having dummy functions.
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1462454674-2246-3-git-send-email-noralf@tronnes.org