dt-bindings: add vendor prefix for NLT Technologies, Ltd.

NLT technologies is the former NEC display business, but changed its
name to NLT Technologies when forming a joint venture with
Shenzhen AVIC OPTOELECTRONICS, Ltd.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170608180758.31020-2-l.stach@pengutronix.de